I have a 16' aluminum boat that I've been using for a while and I want
to customize some things on it, such as rod holders, downrigger mounts,
etc..

My question is do I need to take off all the electronics, including
30hp outboard, from the boat so that the welding doesn't affect/fry any
of the electronics?

My assumption is yes, get everything electronic off the boat.

Also, what alloy of AL should I be using?