Katanas and Ninja Swords are a bit of an oddity. Katanas pop up infrequently, but most likely in the order that they're listed in the License. The only way they wouldnt be is if you simply passed one of their spawn chests without realizing. Ninja Blades come into play once the map opens up. They can be found in a very confusing order if you're not using a guide.

Accessories are like Katanas. They're typically put into the game in the order that they're unlocked, but some of them are increasingly difficult to find as you move on. For example the first Jade Collar can be acquired very early if you know where the side quest to get it is. Same with Golden Amulets and Embroidered Tippets, they're on unlock 4 or 5, but seem like a much later item to be found. However the first Golden Amulet is found 2 zones from the first time your party is 100% complete. An embroidered tippett can be found in a chest that spawns only 25% of the time not long after you've left the Golden Amulet area. Plus is you can reach the tippett you can acquire the other 2 Golden Amulets easily available. This will keep all 3 inactive members of the party doubling LP.

I agree with everyone else. Just unlock what you need or have. If you have the LPs item it'll be in white instead of blackened lettering. I usually prioritize unlocking HP and Battle Lores. Mages obviously I unlock channelings and Magic lores first. However there's more than a couple of chances for you to make LP pointless. You only really need about 2k LP to "complete" the boards. This can be done most effectively (imo) by rushing to Ozmone Plains, Field of Light Winds and farming Zaghnals with Aero or Aero Motes. You can easily set yourself up her with enough LP and experience to trivialize a lot of the game. However anything below level 60 and the post story content will still be difficult without proper knowledge and know how.