Very sorry but Ive just came back after a break, but seeing how no1 else has replied, let me try lol!
1. Behest....i now believe the behest warden man thing tells you the recommended level now. but for around uldah, drybone 10, horizon 20, nophica wells 30 and then ive only done iron camp lake near limsa for lvl 40.
2.Trading, i think Uldah would be the best place for the market ward. I dont see very many actually 1 on 1 trades, but yea uldah market wards.
3. Uldah by a mile, its the centre of the game world, makes sense.
4. Again, i dont know this one, as i have yet to do a dungeon. I do know that you need an LS to have a good chance at leveling and dungeons, it means not having to wait around for shouts and what not.
So yea, sorry i couldnt be much help, just no1 else was replying, so mayb this will jump start some decent replies! If you dont have an linkshell and are lookin, then please /tell Perito Pulsar in game and i will hook you up. My ls would be more knowledgeable than me, as im only really back myself after a wee break.
take care x