I've played almost this exact same character.. (it was my "ultimate character"

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With 1 *learning bonus* (Shaolei Master) in Ninjitsu you can get that skill up to 17-18 practically in a normal game. Past 12 however you won't notice a great deal of difference (its there, it just not great).
Ninjitsu works rather like dual-weapons.. maximum aggression, EXCEPT that you'll need to pull back after a bit and then "dive in" again (which is VERY similar to the fighting style of moonbeasts). You'll want a high parry skill level AND a fairly high heavy armor skill level (..though of course the same could be said for any character, but more so here). BTW, though I'm not certain, I *think* that a higher level of any armor than whats needed for that armor, provides a small bonus in damage reduction.
You can get blast nova via a chest "drop" without the mage class.. but you won't have access to it as early (the same goes for most spells), and having access to it at all is NOT guaranteed. In any event, poison cloud works great against large numbers of opponents, allowing you to cut through them with ninjitsu attacks (it isn't instant gratification like blast nova though).
The requirement to achieve 5 levels in light poles (even without a learning bonus) is pretty low for the Valkyrie.. so it doesn't really matter if you go for it first before getting the Monk class. Note that I found the Valkyrie class a LOT easier to obtain than the Monk class (especially because I was trying to kill the head monk guy at just the right moment to get the winter shurkien). What I WOULD recommend is getting the Monk class and the winter shurkien before entering the Elven trials - it makes knocking-off most of the elven masters a LOT easier.. BUT it requires a level 7 in magic weaponry.
The "killer app" for the Shaolei Master is Critical strike (with no learning bonus). Its difficult to move past 10 in this skill.. and frankly it isn't that great.