Your word description of your setup doesn't make sense, do you have a diagram of what's hooked up where?
Anything you run straight from your car battery should have an inline fuse near the battery. Amp rating of the fuse can only be figured out by you, since you are the only one who knows what you're running and you are the only one who can stick a meter to it and find out for sure.
If you drive your car regularly, your battery should be fine.