Hi,
as a thief (that does a lot of escort work) I can try to give some hints about needed Lvl:
Be sure to be able to handle all mobs along the trading route, even a giant gangbang. Dead hunters are no help for any trader ;-)
Be sure to know the way your trader has choosen! You'll have to tank/ distract enemies for your trader to escape, and you'll need to find it fast again, it may be in new trouble ...
Maybe try to do some escort jobs without job item equipped? It's by far more easy - have your ID card ready, but don't use it if not needed!
I know that a low lvl thief is a welcome target to most bored high lvl hunters and traders passing by, and I saw some little hunters getting slaughtered over and over by bored higher lvl thieves - thus I'm usually carrying an ID card, too, to be able to help even if it costs me some of my thief XP ...
Wearing job suit makes you vulnerable, and unlike a thief you need to wear it all the times to collect job XP.
Another idea would be to try thief job first - this would give you a nice opportunity to learn things from another point of view first.
About build: Hunters need to kill fast and tank well. 'nuff said.
In case you're on Babel: Please don't attack me if you happen to see me in suit - I hate beeing forced to kill anyone! Be assured I didn't kill anything for my loot - I'm the zero arrange points guy ;-)
(Click to enlarge)
You might come to help me, collect job XP on my NPC thieves, be protected by my harmony circle and rezzed, if needed. Or you might attack a poor loneley thief riding into the sunset on its transport, only to realize that even a pacifistic thief might have an not-so-pacifistic mean bow ;-)
So do some more grinding, get comfortable with the roads from Jangan to Donwhang, learn how to do the job, and don't forget:
Have fun!