The only way to know for certain is to put the car on a dyno. But since you didn't mention which header and exhaust you installed, my guess would be anywhere from -5 up to +10 ponies from bone stock ( and it would have helped if you had the vehicle tested before any modifications were done as a bench mark ).

Probably looking at around 220hp with the cold air intake and new exhaust. But I could be off by 10hp either way with the info you have given.

You would need to take it and put it on a dynamometer to get figures on hp and torque. If the car feels like it has more power...then it does!

20HP max, probably closer to 10, not worth the money you spent on it.

I don't know much about cars so bare with me here... and speak in terms I'll understand. Sorry. Anyways, I recently bought a 2002 Acura RSX Type-S and I think the factory horse power is 200? I also got wrapped headers put in and a cold air intake system thing installed along with a new exhaust. I'm not sure on the details of these things, sorry. There is also over sized 18" tires if that makes a difference. How much horsepower do you estimate the car has now?