I could see quite a few job classes fitting for you at times, and seems rather redundant now...but I think I'm leaning a lot towards Thief as well. Thief characters such as Vaan, Locke, Zidane, and Rikku tend to be pretty open-minded and can be described as artistic (or rather creative, at the very least) in terms of their thought processes at times. A few of them can be a bit selfish as well (such as Yuffie, though she does intend to put her selfishness to good use for her town! XD)...and quite a few of them can be rather arrogant in a way too (Yuffie and Edge are prime examples of this at times). A few of them even do have some insecurity issues at times too (Vaan when he realizes he is in way over his head at parts in FFXII, and Zidane when he realizes the truth about himself are good examples of that). While some of them are more outgoing in nature, there are quite a few Thief characters who fit more of the middle ground between outgoing and reserved too. Quite a few of them tend to be rather cheerful by nature, tend to be more supportive though they can be leaders (such as Edge, Zidane, and Vaan who all display leadership capabilities at points throughout their stories), and I could actually see a few Thief characters agreeing with your sentiments on confidence and modesty too! They tend to be more impulsive, though they do have cautious moments when situations are really dire. And quite a few Thief characters are also rather energetic too. I could see quite a few of them relating to your thoughts on group-work as well, and for some reason I could easily picture characters such as Vaan, Locke, Edge, Zidane, Rikku, and Yuffie in particular really wanting to perhaps secretly become stage magicians or learn how to do those types of things! :D

Also, yay for FFXI love! I had a lot of fun playing that game, and I love a lot of the characters (it's awesome that you mentioned Aphmau as being someone you relate to! ♥). And Layle, Terra, and Kain are all really neat characters! :)