200-250 is a good amount for a trueno.
Other cars.. well, lots of D1 cars have 400 to over 500 horsepower rx-7s and skylines.
Use whatever power you feel comfortable w/. Most big HP upgrades reduce engine response so its probably best to stay under 500 hp w/ most cars and w/ super light cars like the trueno, maybe a little horsepower upgrade to keep the car from loosing dropping out of torque band when drifting. The rest is just skill and control.
I suggest NA stage 3 for the SS trueno and some light tuning.. I have just about everything else "stock" on it.
The best thing to do is drift a car stock, and push it to its limits, and then ask yourself what changes could i make to this car perform more to how i would like it to. More power? more oversteer/understeer? Does it feel too heavy? Breaks too strong/too weak? suspension too soft/too bouncy? and make changes accordingly.