I am a Physiotherapist and noticed that lots of my friends were developing problems with necks, backs, elbows, etc. I started quilting about 7 years ago and it has become a passion so I could also understand why my friends were having pain. Some people that I have talked to seem to really like it. However the way that I look at it is that if you are sitting in a proper chair that supports you well you will have better posture.
Some people use the same table height for both cutting and sewing machine.
There is no way that will be good for you. The best chair is one that fits you personally. Proper level includes body type, lenght of legs, depth of chair etc. Sit in lots of chairs before you buy. Macnine quilting is especially difficult because you are often very tense.