Some of your questions can be answered by doing a Google search. As for a SIM card, likely you can use your phone same as you do in Europe, but don't know if anyone can call you? Do you use Line or Messenger both of which are common in Thailand.
Many years ago I had a lad who offered to rim me and I readily accepted; it was great. As I recall it was at a massage shop and this was part of the service.
The Thai expression for rimming is "clean/wash the refrigerator". Sounds like "laun tu yen". They all understand this expression.
I might add that "they" your boy du jour, often enjoy the experience if you offer it to them.