Anyone have a theory as to when it's best to become a ninja? I read somewhere that you should try out a lot of other classes before fully developing as a ninja. Is that correct?

I was thinking of doing something like this:

Priest (up to level 4)
change to:
Barbarian (focus on thievery skills, up to lvl 7)
change to:
Ninja

Should I change to more roles before becoming a Ninja?

I think the worst option in your proposal is that for so much time as a barbarian you can't learn any magic. You can still train in locks and pickpocket as a different class (ie at the Pawn shops, level ups) - you just need Barbarian for the skill. I woulld suggest less time as a Baa Baa, and instead some time as a warlock (take advantage of amulets of holding about Ishad and increase your strength to 24), and then very briefly a paladin (when you get to Temple guild 5, so that you can pick up the Crusade trait - very rewarding in skull castle). Then get your Ninja.

Do pay attention in your party to develop Vine magic high enough. You'll want to have level 4 spells in the serpent temple for cure poison, and later level 6 for cure (disease). So keep at least one character priest for long enough. (Rangers can learn Vine magic too, but the quest to become a ranger is hard to solve before doing the serpent temple.)

Man, those posts were nearly a page apart when I answered them - didn't realise they were from the same guy. Would have said - SEE EARLIER POST. Me tired know from terminal brain cell loss and keyboard poisoning - need good ukabu brew.