You got all the good news, now for some words of caution, meant not to put a damper on your holiday plans, but rather in the hope they will go off as beautifully as you hope.
The ambience in Samuis nighttime entertainment areas is as relaxed and freewheeling as you will experience anywhere. The ease with which one gets intoxicated by the excitement is partly due to the island being an exceptionally safe place to let loose and have fun. However be aware that like any tourist destination, we do have our petty criminals and yes - we do have laws. Try not to let your sense of being completely cut-off from the world you know, make you lose your common sense. If you are involved in a serious incident such a drug arrest, robbery, or motor vehicle accident, the downside to being in a land where you are an anonymous stranger, will quickly come crashing down on your head - and hard. Exercise the same caution you would at home, and you are most likely to have a perfect holiday.
Firstly and most important, if you going out drinking for the evening, leave the rented scooter home, and take taxis. While the statistics on the number of tourists seriously injured or killed every year on Samui are not commonly made public, they are shocking. There are a great many people driving bikes and cars while under the influence at night on Samui, and driving them too fast. Again - leave the bike at the hotel.
If you decide to pay a new friend for her (or his) company for the night, needless to say, wear a condom. The vast majority of those on Samui who are these days called "commercial sex workers," do not have criminal intentions of any kind. In fact as a group, they are about as honest as people in other walks of life in Thailand. However there are occasional incidents.
In particular be extremely cautious with men masquerading as women. Walking the streets of Chaweng after 1:00 am can be like a science fiction movie. Transvestites and transsexuals ("real" women sex workers do not do this) maraud the streets on scooters late at night, inviting men unattended by women, to accompany them. If you go, you may be placing yourself in a dangerous situation.
If you choose to take a new friend (sex worker, casual acquaintance or fellow tourist!) back to your hotel, always safeguard your valuables. Finally, women especially, are strongly advised not to accept invitations from a stranger to walk on the beach at night.