Yes, for sure you can start Massage Therapy Business at home for this you need some important things like license, equipment, practice, etc, but yeah! you can start it at home.
If your business is growing then you can't do everything by yourself, you have to hire some staff so that everything should be done in a perfect manner. But , if you have started recently then you can do it alone.
Numbers may vary according to the region but the first thing you have spend on is having a place , taking place on rent will cost you differently in different areas, after there are many things for that you should check the article.
Yes if you're starting a business then you should surely have a separate business account to keep your personal & professional things separate. Also, it'll make your business looks more legit
Yes, any business can be expanded at a larger scale the only thing required is hard work & a vision to grow.