Re: what kind of amp should i use??
Super expensive amps aren't needed for a subwoofer. The small amount of distortion in a decent quality amplifier will not be noticed. You don't need to spend a fortune. Kicker, Alpine, and JL are good brands to look at for amps. If you will buy used, then look into old school Zed-made amps. Great quality and dependability, and you can usually find them at very low prices.
Running fully active with US Acoustics 4050 and 4060 Zed built amps
ID OEM 6.5" mids and Seas 27TAFNC/G aluminum tweeters
12" Dayton Titanic in 1.2 sealed powered by HS 2.125