If that is the way you want to wire it, that is fine. However, you do not want a 30A fuse going to your lights or other accessories that use a small amount of power, as it is a fire hazard. just so you know, lights are usually 3A or so, radios, fishfinders, GPS are generally 2A or less, a horn will be higher amperage, say 5A.
I also like the convenience of a master switch on the dashboard. I am pretty good at turning the ign switch off, but sometimes I would leave the radio or some other device on. The master switch helps me make sure all is off.