I was looking at the different gear in the game, and figured out what could possibly be the best gearing for a level 1 character, assuming they had the money. This is what I came up with...
15 Def Mod
6 Equipment Slots Used
17 Str
As monks can't use armor, and they only get +5 def every time they take the class, this means they would have to be level 25 to achieve that type of defense based on passives.
If we include enchants, which as far as I can tell, you can only take +15, that would mean that to reach that level of def, a monk would have to be lvl 40.
Now, if the monk is strictly supposed to be an RP class, I understand, and I'm playing him as such. I just thought I would point out a few things that I thought about.
Since Monks can't use equipment, my suggestion would be to have different 'schools' or 'styles' of martial arts that a monk could specialize in when they take the monk class again, and it would give them the +5 def bonus to make up for the lack of armor, but also give them a boost to a specific stat, allowing them to customize their playstyle. It could be as simple as just +dmg or +def, or you could let them have bonuses to specific stats. This way each monk could be unique in their combat style, would still be able to hold their own in fights, and not be overpowered since after +15 attribute points on tattoos, you could plot their progression linearly, and balance it based off that.
Dunno, just an idea.