Your most important factor is amps and giving your speakers enough juice! Headroom is important.
JL makes a terrific amp (their one product I love) and they have a marine line if u want it.
ARC makes the best amps on the Market IMO nowadays. The KS series is a very efficient amp that doesn't break the bank. It's a Class G/H amp like the alpines, which is what gives it's efficiency. Some say a g/h class amp can be lacking in the midbass frequencies... I've honestly heard it, but most never will. I run these amps in my boat.
The Wetsounds amps are great and that piece of stainless is beautiful! BUT they ARE the KS amps above. They are the same amp, but the Wetsounds have coatings on the connections and board. These were originally going to be the Hertz amps, but Tim couldn't get the Italians to get the price down low enough.
Love the hertz amps, but they're $$$$$$
Power is everything... This is the area you don't wanna skimp. A poor amp can make the best speaker sound like crap, and a great amp can make a mid range speaker outperform your expectations.
But once again, tuning is EVERYTHING!