Using just a spoon and fork is not as difficult as it might seem at first seem. Most ingredients in the meals are already cut up into bite sizes before cooking. So, unless you are eating a steak, there is no reason to have a knife. The fork is only there to scoop food onto the spoon which is then raised to the mouth. On no accounts should you put the fork in your mouth. This is much the same as putting a knife in your mouth in Western culture.
When it comes to the time for paying the bill, it is usually up to the person who invited you out to pay. Either that or the oldest/richest person. There is a certain amount of prestige in being able to pay for everyone so let them do it. You should also remember that when asking for the bill in a restaurant you say "chek bill". However, in a street food stall you can say "gep dtung" which is more colloquial. Don't get that mixed up!.
