That stuff in the OP is all nuts and bolts. Now we're getting into the intriguing intuitive meat-and-potatoes shit.
Lights-out relievers are completely fungible. Yeah. Flamethrower bullpen arms are a dime a dozen. They're so ubiquitously available if you know where to look that it approaches house rule territory. You might find yourself picking the erstwhile "closers" with the seven best names.
How? Firstly, they're available in the draft—but not where you'd expect. Sort by "All Batters" and peek at those players' pitching ratings. Oftentimes there will be an absolutely filthy reliever in there masquerading as a catcher or shortstop. Reach for him, convert him to relief, ???, profit.
Failing that, trade for one. Minor league relievers, even exceptional ones, are extremely easy to acquire. There are also almost always quality relief arms available in the Rule 5 Draft. You can either draft 'em or trade their team a pittance. Assembling an elite bullpen is a snooze. New house rule, I think. Don't exploit. Only target the hotshot relievers to which you really take a shine.
Splash the pot on international amateurs every other year. It's worth noting that in OOTP 16 and beyond, you're likely going to have to wait for every third year. It'll still be worth it, though, to lay down tens of millions of dollars on the top bonus babies come available July 2nd. Your signing pool each summer is only $3 million, but since this is a "soft" cap, you can exceed it by as much as you want. Overages are taxed double and you can't sign any large bonuses the following year, but it's well worth it for all the elite talent you'll stockpile. If you're a smaller-market team, it is truly worth cutting costs and limiting payroll so you can afford to woo some 16-year-old Domos.
If you just barely can't swing a trade, convince the AI to accept by including a rookie ball middle reliever, a 30th round draft pick, and $800,000 cash. For some reason, the trade AI loves that shit. Use sparingly, and remember what I said. This is a "break in case of emergency"-type protip.
Use this filter to sign quality minor league free agents during the season. About once a week I sift through the free agency pool with this filter. I sign probably half a dozen of these guys to minor league contracts each year. You'll be amazed down the road at how many valued contributors were acquired in this way.
Trawl the waiver wire every third day. Decent depth options, reclamation projects, and yes, even lights-out relievers will occasionally appear there. Once your claim goes through, you can usually sneak the player through waivers your own self and assign them to AAA. Note that after the July 31 trade deadline, the really solid players that appear here in groups are more often than not part of a waiver trade, and it's best not to interfere. I think this is also in direct violation of the real MLB's "gentleman's agreement," but hey.
"Stuff" is the last thing to develop for a teenage pitcher. High school pitchers will almost always improve their velocity, sometimes by quite a lot. With it, the "Stuff" rating will surge. Target teenage pitchers with good Movement and Control and wait for the Stuff to catch up. As always, keep an eye on their leadership, intelligence, and especially work ethic.
Play the game the right way. Sacrifice bunts are stupid. Hit-and-runs are stupid. Stealing bases is usually stupid. Make use of the "Strategy" tab and avoid these pitfalls. It should end up looking something like this. Copy to all times and situations using the dropdown menu. No idea whether the infield shift thing is prudent ingame.
You can easily implement this for your minor league teams as well by assigning a sympathetic manager to each level in turn, asking for his preference using the same dropdown, and then copying to all times and situations. Be sure to favor prospects more and more heavily the further down you go.
Make use of the "Stopper" role! Closers are stupid. If you're playing OOTP, you may already know this. Closers are stupid. Bill James has been trumpeting the "relief ace" model since the 1970s, and with good reason. Closers don't pitch the highest-leverage innings and are thus stupid.
Head to the League Settings → Stats & AI page and temporarily put "Use of Closers" to "Rarely." Go back to your bullpen and set your best relief pitcher or two as "Stoppers" during the "7th & close games." Change use of closers back to very often for all the other loser teams and your bullpen roles will stick. (They'll appear blank.) The game may change them back to closers occasionally, so keep an eye on it. Otherwise, voila! A far more efficient, new-age bullpen. You're ahead of the curve. While you're here, you probably want to set your rotation mode to "Strict."
Platoon. Whenever you can.
Install the All-in-One Mod. This is really the very first thing you ought to be doing. It is so aggravating seeing people take screenshots of their games sans All-in-One Mod. From ingame: File → Add-Ons Central → 2014 All-in-One Mod. Download then install.
Make use of Questdog's nameset. These are so outrageously better as to be night and day. I can't believe the devs haven't integrated these into the base game. It's almost imperative that you check these out.
Save this image as "wall1.png" and have it be the only file in Documents \ Out of the Park Developments \ OOTP Baseball 15 \ facegen \ background. This is really out there. In fact, I guarantee this is proprietary. But now, instead of dealing with a bunch of arbitrary, busy scenes, your players' headshots will look like the real ones. (Here's Lester IRL.) You probably want to back up the contents of that folder first.
Create your own FaceGens with this software. You know what? This is a test. If you're actually gleaning anything from this, and actually want to know how to use this, PM me, and I'll explain it then. Homemade FaceGens turn out be-a-utiful.
I hate how 75% of the players in this game sport ridiculous Elvis sideburns. If you feel similarly, you can correct this by navigating to Documents \ OOTP Baseball 15 \ facegen \ hair and removing everything except the five "Short" ones. Move them elsewhere, since deleting them is inadvisable.
Go to League Settings → League & Teams and change the Yankees' abbreviation to NYY, the White Sox' to CHW, etc. Pet peeve.
Check out the skins that are available in the main settings. I really love "Classic," which isn't default.
If the game is lagging or you're experiencing trouble, disable 3D effects in the main settings and try playing in windowed mode.
OOTPDevelopments.com houses some more cool shit.
You can exit the game without saving by pressing Ctrl+Shift+Esc. Highlight OOTP, End Task, and wait for the popup. Click "End Now." Wait for the next popup.... Click "Cancel." A mulligan. This comes in dead useful when you're negotiating a contract extension and would like to lowball. OOTP's bartering engine is not exactly robust, and players will break off negotiations at the drop of a hat, so I don't consider this cheating. Save first!
Tell your antivirus to ignore all OOTP directories and disable their indexing as well. This is huge. The game will run demonstrably faster. I'm talking about the three folders titled "Out of the Park Developments" under Program Files, Documents, and AppData\Roaming (accessible if you go to Windows Explorer and type "%appdata%" into the quasi-URL bar). To disable indexing, right click and choose "Properties." Click "Advanced..." and uncheck everything. Speedy!
Clear out the junk in these directories each offseason. Documents \ Out of the Park Developments \ OOTP Baseball 15 \ saved_games, then your save. Empty the "replays" and "messages" folders (the latter unless there's something in your inbox you want to keep). Go to news\txt and empty "leagues" and "teams," then news\html and empty "box_scores," "game_logs," "leagues," "players," and "teams." Unnecessary clutter that certainly does build up over time. It's worth noting that you can back up a save by duplicating that parent folder within saved_games.
The easiest way to develop prospects is to shortlist them and disable AI pro-/demotion via their profile dropdown. Shortlist every prospect you like or care about. Three times a season or so, use the right and left arrows on the profile page to cycle through every player in your shortlist, promoting and demoting as necessary. Whenever any sort of player movement happens at all, go straight to your team's roster afterward and the "Available Actions" dropdown. Ask the AI to set up the complete minor league system. Your shortlisted guys will stay put, but everything else will progress naturally. Do this 100 times a season.
Bookmark all the pages you frequent by using the star up top. Set your start screen as well. These are mine, for what it's worth.
Manually play games with great pitching matchups, rookie debuts, or playoff implications. It's a lot of fun and you get a good feel for your team—as if you're tuning in. Naturally, I play through the whole playoffs. I shoulder the blame for whatever happens in the ALDS and I'm right there for every historic hit.
Dude I'm pooped. Are you happier now? Go play OOTP or something
