I have an old jacuzzi tub - just the shell. The plumbing is in rough shape, but have a good filter, water pump and air pump. I would need a heater too. I don't even know how to support the shell, wether it is supported by the just the rim, the footwell, or both.

Any suggestions? The tub is a 8 person shell.

proper support for hottubs would include supporting the footwell, and the rim. What I do is set the tub on level surface, meaure each of the corners to the floor, and take the average of those measurements and make my sides. It's a good idea to put the footwell on some styrofoam insulation to help prevent heat loss, and if you do this, do it before you take your corner measurements.