After dealing with the complex power system of my PDQ, installing a surplus panel on my F-24 was the work of a few hours and few dollars.
The panel. I like rigid panels, but semi-flexible can make a lot of sense for small boats. The key is that they should not be stepped on, no matter what the vendor says. They use the same silicon cells and they are fragile. Also, they should only be flex once, during installation onto firm support. A bimini is by definition a problem, a common cause of premature failure. The typical story is that "it was a great installation," and then several year later, "I need to get better panels; these didn't last." Of course they didn't. They flexed in the wind and the cells developed thousands of microcracks.
Open circuit voltage of a "nominal" 12 volt panel is about 20 volts. The moment it is attached to a load that drops way down.
Location is always a conundrum; where on the boat never sees shade. The answer, with sails up, is that there is no such place. Since I hate arches and the F-24 is a sport boat, flat on top of the slider was the right answer. It's not under foot and the boom can be swung to the side to leave it clear at anchor. Another advantage of the slider location is that the screws are not into corred deck and thus leaks are unlikely.
There is no need to mess with the main panel. Solar systems wire direct to the battery (or studs that are directly connected). They should NOT be isolated by the battery switch. However, you will need a fuse. A simple in-line fuse is fine.
Wire size need not be large for a 50 watt panel; #14 AWG is enough. With larger panels you need to stay below about 3% voltage drop.
A simple automated charge controller can be had for $25. Two wires come from the panel, two go to the battery and fuse. Generally they are smart enough to sense the battery and type, regulate bulk and float charging, and schedule equalizing. Wow.
I could write pages about good wiring practices. Use a ratchet crimper, adjusted for the fittings you are using. use grease on the contacts. Keep things neat. And don't forget the fuse (panels are known to short-out). MC-4 connectors are very good in a marine environment, but I always seem to cut them off and just crimp things together; the pigtail length is always wrong, the replacement panel will be a different shape, and they don't actually aid in troubleshooting.
It couldn't be much simpler these days. If you've got questions, just ask.