Re: How many circuit breakers/fuses to I need?
If you are redoing, I would replace what's there with the same size fuses/breakers. The rating of the fuse/breaker should be on it. The rating of breakers and fuses are expressed in amps, basically how much current can pass through the fuse/breaker before it blows. Each application is different, but the size of the wire (conductor) is the biggest factor. You don't want to use a fuse/breaker larger than the max amount of current the wire can handle. That being said, it is quite common to use a fuse/breaker smaller than what the wire can handle, but slightly larger than the maximum current draw of the device. This way, if there is a problem, e.g a short circuit or the device starts drawing too much current, the fuse/breaker will blow before the wiring is damaged.
Without knowing more information, it's impossible to say what size fuses/breakers you need. Just keep in mind that if a fuse blows, it needs to be replaced, so it's good to carry spares. With breakers, they come in two varieties: manual and automatic. If a manual breaker pops, you must manually reset it. With automatic breakers, they will automatically reset... But if the problem is not fixed, they will pop again (and this cycle will repeat until the problem is fixed).