Enchantress' skillset is set up for early domination and, in 95% of games, that's going to be what you bring to a team. Bringing two jungle creeps to a lane for a level 1-2 gank can be very, very effective - she's probably the best early jungle ganker for this reason. Up to the midgame, Untouchable and Nature's Attendants make you nigh-unkillable by all but the burstiest of opponents, and through pushing you can ride your wave of momentum to the late game...
...Where you suck. Pretty much always. Your stat gain is terrible, and Untouchable and Nature's Attendants become way less valuable as the game goes on. You lose easy access to jungle creeps as carries begin to farm the jungle. Two of your abilities are taken up by personal protection, so you don't even really have any team utility or carry potential to bring to lategame teamfights (unless you're stomping HARD, in which case you'd probably have won with any other hero). Your job at this point is to Enchant an Alpha Wolf, sit back, and occasionally throw Impetus at enemies without dying.
This is why I tend not to recommend Midas. Enchantress is always going to be a bad character in the late game unless she's somehow managed to get a 1-2 item lead on their carries. Don't bet on the late game, because you will lose. Instead, buy items that help you keep the early snowball going for as long as possible.
Hotkeys: I keep mine simple. 1 = Hero and Creeps, 2 = Hero Only, 3 = Creeps Only.
Ganking: You'll most likely be closest to your safelane, which is incidentally also one of the easiest lanes to gank. Enchant 1-2 jungle creeps and approach from as far down the lane as possible. Send your creeps in first (press 3 to move them into relative position and then 1 to move your units as a whole). Tab through your creeps to use their abilities, then switch back to Enchantress. Hopefully your target is dead.
Example: I'm Radiant Enchantress. I Enchant and clear two camps, grabbing a Dark Troll Summoner and a Centaur Conqueror. I send the creeps ahead of Enchantress, then select all while maintaining primary controll of the Troll. I tell bot lane I'm coming. I wrap around bot lane, entering at the point just below the entrance to the river, and Ensnare my target. I then Tab to the Conqueror, move him in close, and War Stomp. Having used my abilities, I switch back to Enchantress and attack until dead.
Same basic logic goes for ganking mid, except it's a lot harder due to the shortness of the lane and the prevalence of wards on either side. Use a Smoke and wrap around from the highground on the top side of mid (both towers are positioned closer to bot and will spot you out and start firing if you approach from there). Wait until the gank target is forced into the river to last hit and he'll be a lot more vulnerable.
Keep this up. Seriously, as much as possible - this is your time to shine as Enchantress, so make the most of it. If gank opportunities are seriously lacking, then stack jungle camps in your spare time, and if you get a Wildwing Ripper, farm camps with its Tornado. This will give you a significant boost to your gold and EXP but this is NOT the best use of your time. It can be tempting to stay in the jungle farming stacks with your Wildwing, but remember: your entire purpose as a hero is to get in opponent's faces early.
I hope any of this is useful! I'm a pretty terrible Enchantress, but I fail mostly on execution rather than the theory I think :D She's not a simple hero to play, and she can be very easily counterpicked (burst of any kind wrecks you forever) but she's a lot of fun!