whould adding a under crank pulley and a cold air intake be the best next step to take after adding tints rims muffler and taillights? would that cause any problems for my car?

 

the cold air intake wont hurt your car. it will give your car more power and better fuel economy. the underdrive pulley wont hurt it either, but you might stall out due to less spin on the alternator, wouldnt really worry about that unless you have a powerful stereo with subs. sounds like a great next step