Need Some Help With My Civic Performance

I would be really thankful to anyone who would like to help me with my 2001 Civic LX.

Im having trouble deciding whether to work on my intake or exhaust right now. I have a budget of like 300 and i would like some ideas on what i should do. If im working on my intake im going to buy a Intake kit something like AeM cold air intake unless someone has a better idea ( suggestions? ). And if i go Exhaust im thinking of buying a muffler ( not sure which i should buy ) cutting my old one off putting it in place and taking the catalytic converter off ( not sure if i can do that yet cuz of sensors and stuff ). I would like to put a header but i asked my dad ( mechanic who thinks he knows everything ) if a header would boost my hp much and he said it wouldnt ( would like some feedback on that ) thankx