I stayed at the Crowne Plaza. Great hotel and had a great time. No problem at all with joiners. It's just a short walk up the hill to Blue Boy. If that's too much, the monorail has a stop right at the hotel and gets you there in one stop. It's good because you also get the monorail from the airport train.
Hundreds of gay guys from many ASian countries attend the full moon parties. Not sure if there are any dedicated gay areas, but since many guys go in groups, they tend to gravitate towards each other during the night. Don't worry. You'll have a blast.