What do you recommend? Trunk Battery, like to put a inline fuse. what size?

The starter draw is the highest load. You would need a battery load tester with inductive pickup amp capabilities to see what your starter is drawing while cranking. As starters age/wear their amp draw increases so your fuse or breaker will need to be larger to cover the added draw. Your starter may draw a couple hundred amps. Old starters may draw 4 or 500 amps. It all depends.