Use the teflon. Don't over tighten. Check it out after a few days. If it it leaks
at all there will probably be some green on the bronze. Tighten a wee bit more. This is not a hot or high pressure joint so sealing will not be severely tested. If it does go belly up, shut off the valve and try again. That's what the valve is for.
I had two similar arrangements and got away with a bit of petroleum jelly. No leaking after ten years.
I am not sure that the plastic hose tail needs to be an expensive one. The thread is under compression
as it's screwing into a female thread so it is "safer". Not under any real load unless the hose is moved around too much.
I would be more concerned with ensuring that the hole cut out for the valve skin fitting is absolutely water proofed particularly if the hull
is composite. Don't spare the epoxy
Use a proper marine
sealant under the skin fitting and under the inside backing plate. Not silicon.
Re brass or bronze. Brass is for garden plumbing and fresh water. Bronze is for boats. (The exception being LPG gas or refrigeration
, where there is no (hopefully) sea water.) Use bronze only. Do not mix brass with bronze as the zinc in the brass will "leave" in very short time causing all sorts of problems. Bronze skin fitting, bronze valve.
When using the loo, it is important that you can sit back and admire your plumbing.(sic) That one may not get past the moderator.