In the clinics I work in, clients are told to wear whatever is comfortable for them. When a client is brought into the treatment room, the therapist will instruct the client to undress down as far as they are comfortable. Most clinics have clients leave underwear or panties on and take everything else off, including jewelery. Spas may have a changing room where clients will undress and put on a robe to go to their treatment. It is individual based on the clinic. If in doubt, always give the clinic a call and ask them what you should wear. They will be more than happy to explain their procedures.
Generally you are nude, but you can wear underwear, especially for women who are menstruating.
During certain types of massage you can such as Thai massage, Shiatsu or chair massage.
DICK?
Yes, you are allowed to wear whatever makes you the most comfortable. There are massage styles where the recipient remains fully clothed the entire time.
You wrap yourself in a towel.
You can wear whatever is comfortable for you.
Generally you are nude, but you can wear underwear, especially for women who are menstruating.
No, you do not have to be naked. You can wear underwear, but women do need to be topless.
When you get a massage of any kind, it is not necessary to be disrobed of all your clothing. Not even a French massage. Some modalities are performed more easily if the cloths are removed, but this is not a requirement and no professional massage therapist will ever force their client to do something they are not comfortable doing, even removing clothing.
Every massage therapy practice has their own set of expectations. For example, in our practice we tell our clients to undress to their level of comfort. I tell them that I have worked on individuals that are fully clothed and individuals who are the complete opposite. I believe that most massage therapists want you to feel comfortable and not be nervous. I have been to massage therapists who do want you to remove everything before laying on the massage table. If this is the case, I have always seen instructions in the intake paperwork explaining the benefits of massage therapy and why they would like you to remove all clothing. If you are unsure, don't hesitate to ask your massage therapist. They will be happy to answer your questions.
No, not particularly, although many choose to wear medical scrubs due in part to their requirement in many massage schools, as well as the fact that they are non-constrictive. Different Therapists have differing opinions on the matter, however, they will all agree that plain clothes are far too constrictive.
No, tampons should only be used when you're on your period. Never use when not menstruating as this will be uncomfortable and potentially increase your risk of contracting Toxic Shock Syndrome. There's absolutely no reason to use tampons when not on your period, having a massage makes no difference: there's no reason why you should need to use tampons while having a massage.