Regarding your concern:
1. You can wear anything comfortable. In the event that you need to change, they will give you robes and shorts to wear during the massage. Do not worry as you will draped respectfully during the entore therapy session. Only body parts (except private areas) which are being worked on will be exposed.
2. What body part do they massage? If it is Swedish massage, they will massage your whole body (except private areas). if it is Indian head massage, then expect to be massage only on the head, nape, and shoulders. It actually depends on the massage modality that you will choose.
3. You can actually choose but generally, more female massage therapists are working in the spa so, most probably it would be a female. But if you have certain gender preferences, you can ask beforehand. Call the spa to be sure.
4. No.............they do not massage balls or any private areas.
Maybe this article will be able to help you select what massage is right for you, just click on the link
This article will give you the glimpse of massage therapies
The Basics of Massage Therapy (Massage 101)
http://yunesa.blogspot.com/2009/02/basics-of-massage-therapy-massage.html
Hope this helps a little.
Eunice