If you're wondering if you should do a heavy gauge, like 8 gauge, there really isn't a need. Large wire is helped to reduce resistance, but with the current you'll be feeding the sub there shouldn't be any issues. Standard 12 or 14 gauge wire would be fine.
do u like matching gear? is so go with http://cgi.ebay.com/KICKER-08-ZX400-1-CLASS-D-AMPLIFIER-MONO-BLOCK-400W-AMP-/130 391365182?cmd=ViewItem&pt=Car_Amplifiers&hash=item1e5bee563e this kicker 400.1. one more question why do u want a kicker l5?
If you don't already have the sub, just let us know what you're looking for out of a system and we can give some advice. If you wanted to run a single 12 or 15, you could do a Type R in a ~2.0 cubic foot ported enclosure, tuned mid to low 30s and it would do well on ~500 rms. Affordable and impressive. The L5 will get loud and shake your car, but thats about it. It isnt going to have much musical ability to it.
I'd try and sale that kicker and get two alpine type r 12's and get u a pretty good amp from around 1000rms to 1200rms those type r's will run you about 130 a piece but they are good subs! For a amp and your price rang either a aq1200 or ask Kevin for the rd1000.1 or last option go with a hifonics Brutus amp I've owned one poeple say they are not that good of a amp but for how much u pay for it it's pretty good amp! And don't forget the box means the most in a system get a ported box I'd recommend
Yea,i think id try to sell that sub too. Ive had a set of L7 10s an while they did get loud,they didnt sound good at all. BUT... If your not into that,just buy a second 10'' L5(dual 4 ohm) an get yourself an aq1200. http://www.audioque.com/aq/?page_id=26 Also, a good box is key. Build one,or have someone build one for you. Good luck