5200 is considered a "permanent" adhesive/sealant and thru hulls sometimes need to be removed for inspection/replacement. I would use 3M 4200 or even Dolphinite, especially for an above the waterline application. We curse anyone who has used 5200 on items that have to be removed. You have to destroy things to remove them. Use it as an adhesive only!

Your thru-hull was 6" above the waterline so nylon or equivalent is more than adequate but bronze really doesn't cost much more so I'd use that instead.

Using quality clamps and hose is just as important as the thru hull and a siphon break is a good investment.