You should be okay with them. A 5kw unit will work, but a bigger one would be better. The real wildcard is your batteries. How big a bank you want, and what type of batteries you get.
All the big players in turnkey systems are putting out a decent product. Enough units have been installed that by now everybody has worked the kinks out of the design and tooling and materials. There was a time when this simply wasn't so, and buying a complete system was not IMHO a good idea. Now, it is worth considering, and there are a lot of satisfied owners even on this board.
Myself, I cobbled my system together myself, for less than $2500 including a 10.56kwhr bank of golf cart batteries. No solar yet, but there will be, when I have the money. I am happy with my setup but I put a lot of time into research, sourcing components, and putting it all together. DIY is not for everyone. With the turnkey systems, the engineering is already done. Just mount, couple, and connect.
Everyone has their favorite battery technology, but it mostly boils down to LiFePO4 or flooded lead acid. A few guys like gel cells or AGM because you can mount them any which way. I don't like them. Too many things can go wrong with them that you can't remedy. Flooded cells need to be topped up with water occasionally. They should be equalized a couple times a year. They should remain above 50% charge, though an occasional dip down to 40% or so is not the end of the world. LiFePO4 batteries rely heavily on the BMS to prevent thermal runaway situations. The technology is now mature enough that it is a viable one, and it has many advantages. Higher usable power density. Longer life. Less sensitive to deep discharge. But much more costly. And needs careful monitoring especially during rapid charge and discharge. That's when stuff happens. Or when there is physical damage that shorts out a cell. I think overall lead still wins, but if you have deep pockets then Lithium is worth considering.
Another question with batteries is how much capacity do you need. For a lot of sailors, those who SAIL their boats and practically never motor except for docking, a fairly small bank will do just fine. Four group 31's in series, for instance. Maybe a separate 12v house bank, maybe not. You can run your 12v loads off a DC/DC converter and just have the one bank. If you motor a lot or carry a lot of house loads, then something like I have, 8 6v 220AH GC2 golf cart batteries in series might be just the thing. I paid $85/ea at Sams Club for mine, over 3 years ago. Still going strong, better now than when they were new. However, I know how to maintain them. Some owners will see their batteries going tits up at the three year mark and wonder why those batteries suck so bad. A lot of it is the maintenance. There are bigger batteries, too, if you really need a lot of storage, like L16's for instance, but that might be pushing it on a 31 foot boat. Still worth a look. But GC2 is probably the best bang for the buck. There are also single cells up to 2000AH and bigger, but you don't want to mess with them. Or even 8D or 4D. Big, hard to handle. Lithium cells come in a variety of sizes, too. Most boats up to 35 or 40 foot use 48v systems. The wiring standards are different when you go above 50v. So if you go bigger than 48v, you may as well go up to 96v or maybe 120v. Of course your motor and controller have to be rated for the voltage. for your boat, 48v is a good setup.
Will you be doing a lot of cruising in your boat, or will it mostly be a dock queen and weekender? Do you motor a lot, or a little? Do you like to tinker, or do you just want to twist a knob and go? Do you have a diesel, and will you be keeping it or pulling it? Have a generator?
I suggest getting your bank in, first, followed by the motor and controller and user controls. THEN worry about solar. The cheapest way to charge is not from solar panels. Its shore power. For now, anyway. But solar charging makes you much more flexible and independant.
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