@Lion ...you first need to decide what you are looking for in a system. Great sound at all volumes, listening at rope length, listening on the swim deck, or owning the cove (sandbar in my case). Let is be said that the JL Audio "HD” line of amps is pretty much the pinnacle of marine performance when properly applied. I personally run Wet Sounds SD amps which are also top of the line, efficient and vert powerful. However, I also know that these are out of budget and overkill for a large percentage of folks. Truth is, when properly set up, good marine mid-level amps are going to satisfy most. My first setup had three marine Rockford prime amps and it sounded outstanding. My first advise would be don't skimp on your interior speakers and your wiring. Make sure you run a large enough power wire to allow for expansion. Also, depending on your listening style, figure out what you think you'll need in batteries and get that stuff squared away first. On the subject of combining Rev 10's and Rev 8's....don't do it. The 10's not only sound better, bit make sound more efficiently. Go with the same whether it's 2 or 4. There are so many options when it comes to using channels on particular amps...just remember...REV speaker need lots of power. I'd say an absolute minimum of 250 clean watts (300 and up would be better). I run a two channel SD2 to my four REV 10's for around 310 watts each. Maybe an SD6 could work for your in boats and sub? 4 channels would be on the 8 speakers at 2 ohm stereo and the last two channels bridged for 585 watts to your sub? Possibilities are endless. Not sure where you boat, but if it's on a lake, some people get away with not using Marine amplifiers. In that case you could look towards ARC audio. I've heard great things about their equipment, and I also understand they're similar in design to wetsounds.
