1. We have a Highfield PVC RIB since 2014. Very happy with it.
2/3. We are an SM so a bit shorter.
4. Don't do it, one decent wave from the stern or quarter and the weight of the water that fills the dinghy hull will break something, maybe your dinghy, but maybe the davits too. We stow ours upside down on the aft cabin roof. We have an elasticated Sunbrella cover that was custom made to fit the dinghy and it is held down on the two rails with two wide webbing strap ratchet tie downs. We have not had an issue with that in 15,000 miles of pacific voyaging so far.
5. Ours is PVC and because it is covered a lot of the time we don't see an issue with UV, however, I regularly clean the PVC and protect it with 303 protectant..it still looks like new.