I went to a few FMPs in my time, so my opinion based on experienece:
No need to stay in Hat Rin, and the hotels there are IMO a scam. Before covid some required extended time there before and after the party.
Most resorts elsewhere provided transport to and from the party. If the Had Rin Queen is still operating can stay on Samui and go over for 24 hours.
My advice- do NOT use the speedboats from Samui.
When I was staying in N E Phangan I took the coastal ferry down, slept on the beach and ferry back next day.
That time of year best to book resort if you are not familiar with that area.
MY BEST advice is not to do illegal drugs there. The dealers apparently inform the cops who they sold to, and there are usually casualties that took bad drugs. Buying oneself off a drug charge isn't cheap and the cops have 2 years to make up for.
Also, if up for a bit of the other, watch out for the katoeys that look for drunk guys to roll.