If you have never driven a 500E before, have you driven any 124 chassis, or any Mercedes for that matter? If not, spend some time behind the wheel of at least a 124, if not a 500E or two before jumping in. Plus, this will help you identify if a car isn't running properly. If you don't have some frame of reference it can be difficult to know what's normal vs wrong. It helps if the indy shop is intimately familiar with them, as I believe the owner of TGA owns a supercharged 500E.
BTW, welcome to the forum!