Once you get to level 15, talk to kreia to get your prestige class, other than that, dont worry about holding back on levels. while holding levels back on the first one was advantageous, doing so in kotor 2 is pointless, as all youll be doing is delaying all the neat stuff you get as a prestige class.
my sith marauder is a killing machine, hacking through hordes of enemies my other companions sometimes struggle to defeat. that valin darklight (my char) crystal is niiice.