The traditional way to wire up small loads (i.e. "portside cabin lights
") is to run one breaker, one duplex power cord, and then yes, parallel all the lights
on that run. So you might have a galley light aft, a bunk light midships, a v-berth light forward, all run from one circuit up the port side of the boat, with a second similar run up the starboard side.
There's nothing wrong with that really, it cuts down on the amount of work, parts, and expenses. If any one light fixture were to short out, which is the only way they could overload the circuit, it would just take out the lights
on one side of the cabin. In theory, some bozo could sneak in and perhaps put 30W bulbs in where you had 10W bulbs, and overload it that way. But with LED fixtures especially...ain't gonna happen.
Remember George Carlin's routines on "Too Much Stuff!" and don't be afraid to gang several small loads on one circuit. As long as the wire is heavy enough so that the one fuse/breaker can protect the wire
having multiple small loads should be OK.
The 78xx and 79xx series regulators can be problematic. They are "dumb" i.e. they regulate by consuming voltage, and they typically have a power limit around 1-1.5A assuming a proper heat sink and thermal limits
. Very convenient, but also wasting a lot of power. (Spend a buck, buy one, hook up an ammeter to see what the waste is.)
Offhand I don't know what they consume but I'd prefer a second 12-volt bus with a more efficient DC-to-DC power converter feeding it up front. Or, just keeping everything on the boat at the same voltage--which can also prevent accidents.