Mez,
I would personally not do hot stone massage as a mobile therapist.
firstly, you have to carry the stones in, place them somewhere and then find an electric point and put water into it.
the stones take 20 minutes to heat up, so yes, its do-able, by the time you've set up your massage couch, and then all of your towels.
you will have to cover whatever you have placed the stones on, I would suggest a flat sheet (single bed sheet) that goes all the way to the couch, therefore if you drop water on the floor you cannot be later accused of staining laminate or carpet.
when you are doing the massage you will need a large bowl to put the used stones in.
after you have finished the treatment you will then have to wash all of the stones, and if its a ceramic sink you may cause a ***** in it (I have done this before at a pamper party).
an hour's massage will take you 2 hours to do, as its set up time, warm up time, washing up then 2-3 trips back to the car.
if you are energetic and have loads of enthusiasm go for it, otherwise, rethink it.
I have a regular hot stone set of 54 stones and a normal size heater.
I would charge £50 for the treatment as you would need to charge for 2 hours work.