+1 to what baileyboat said. Run the smallest amperage you can run without it popping. For instance, if your accessory draws 3 amps, then, run a 3 amp fuse, don't try to run more fuse than the accessory needs, wiring or other components can be damaged.
As for the super bright LED's....they have good products. I've ordered a few times from them, got some LED festoon bulbs for my nav lights, as well as a set of MR-16 LED's for my prow lights. Those MR-16's are as bright as 55 watt halogens, but with a minimal amount of amp draw from the battery. All of the lighting on my jetboat is LED's, including the instruments on the console. I can run every single light on my boat, and there's only about 1/2 a volt of drop on my voltmeter.