Use the stock fuse ratings for the fuses, which are picked for the wiring size as much as the electrical load. Classic burn-bike-to-the-ground mistake. Battery if not new needs charging like said and then use a voltmeter to check the voltage after removing the charger. Then let it sit overnight and measure again (NOT hooked up to anything). A good one will drop a little bit in voltage and then quit dropping. A bad one will continue to drop slowly past a 'set number' to keep dropping lower and lower day by day and WILL give issues, how it can whirl the starter one day and the next only click.
A good battery ranges from a super high of 12.8 volts to a low of 12.3 after the 'sit' and anything lower than that they tend to give issues then. At first removal off charging they can measure a bit higher and a fake number, that is called 'surface charge' and is what the term says, the battery is charged well enough there is a certain small amount of charge that is on the surface of the plates only, it has not had time to soak into the plates to even the plate voltage out yet. Why one should always wait like 30 minutes to an hour before reading the volts, it gives a more real world number. Right off the charger you may easily get over 13 volts which is NOT real. Then the longer overnight sit tells you whether the battery is bad due to sediment in the bottom shorting the plates out to leak power. 12 volts even is pretty much a dead one.
There a voltmeter will pay for itself pretty quick and even quicker if one gets it for free at like a Harbor Freight when they have their free giveaways. You can't work on either car or bike electrical without learning how to use one and WAY easier than most people think. Most people never need more than 2-3 of all the functions those things can do.