Questions:

1--What size (amps) circuit breaker do I need for the key switch circuit?

2--I have a headlight switch that has a 30 amp glass fuse under it---I want to use a 30 amp circuit breaker on it---
Can I use BOTH the glass fuse and the circuit breaker?

3--Is it OK to use both a lock nut and Locktite?

Thank you.