I find 1 to not be true. Escape Orbs work great if you don't care about the dungeon's end-reward. Did you mean Warp Seeds, maybe?
2 and 3 I never even thought of. Thanks for the warning on 2, and thanks for the tip with 3, but I couldn't find a way to sell items to Kecleon in the dungeons. Just drop them on the shop floor?
4 seems pretty straight-forward, Pure Seeds are just so rare in these low-level Magnagates. I hope I find one, and a particularly wealthy Kecleon, in the same one sometime!
The main reason behind my experimentation is to see if the Kecleon behave any differently in GTI than they did in Rescue or Explorers. Seems pretty same-y, though, from what little experience I've had with them in the past.