I'm not sure about the price. I'm not very up to date on pricing on used cars. If it has a CPO warranty, great. Check other online used car sites to get an idea of pricing in your area.
As for the sport pack, I always recommend it. That's cuz I have yet to run across someone on this board who's buying the BMW purely for the badge. People who go on this board tend to be people interested in the handling and performance of a BMW. As such, if they haven't bought the car yet, I always recommend looking for one with a sport package. You get the "full" BMW driving experience IMO. Plus, it's a really good deal. New, it only costs about $1000. Totally worth it considering you get the better looking steering wheel, the much better seats IMO (both in looks and functionality), and all the other Sport Package stuff. It costs a TON more to add all that stuff back in after you've bought the car.
And as for the 323 vs. 325 difference, I say get what you can afford. Performance wise, there's really not that much difference. The 323 had more horsepower, but the 325 had more torque. Or maybe it was the other way around. Doesn't matter really cuz the difference was so small. I only recommend going for the newer engine when it's btw the 328 and the 330 cuz the 3.0 engine made enough of a performance difference to be worth the extra money IMO.