You can have as many circuits as you want, but why would you want to? I recommend against VD’s “Keep it Simple” method of straight wiring to cigarette lighters unless, like him, they are all right next to the battery. The point of the fuse box is to kill the power near the battery so you don’t have hot wires running all over the place.
Most of the 12v marine switch panels are fused at each switch. On my rig I ran a heavy gauge to the fuse block and each panel became a "circuit " with a 15-20A fuse. Then each switch has a 3-10A fuse depending on the load. In theory, I have 24 fuses running the back of the rig.
Based on your avitar, looks like you’re in Seattle. I’m up in the San Juans. I’d be happy to take a look at your wiring diagram. I’m no electrical engineer, but I have a pretty involved system (490W Solar, Inverter, 3 house batteries + 2 Starters on an isolater. all sorts of fun stuff) and have’t started a fire yet…
Lemme know.