My plane has an electrically dependent engine, currently the ignition power comes from the main bus. This means that a failure in 1. the battery, 2. the master solenoid 3. the master switch and 4. the ignition switch could cause the engine to stop (not the most ideal).
What I plan to do is run a second wire from the main battery to a small hot bus which could then power the ignition and cabin lights. This cuts my number of switches that can fail the engine down to 1. My ignitions have 3amp fuses (only one is ever active at a time) and my cabin lights use an additional 2amps. I'm planning to use 18 gauge wire, which is a little bit bigger than what's strictly necessary, but if I ever did have another component I wanted on the hot bus (unlikely but you never know).
I'm curious if this seems reasonable, or if there is something else I'm missing.