Can you afford the initial outlay (otherwise, can you suck up to the bank manager sufficiently to get the money)?
Also, just how busy do you think you'd be? are we talking flat-out 5/6/7 days a week here, or would you be spending most of the day just twiddling your thumbs?
How many people come for geometry checks when they should be in work? Would working a more oddball shift (07:00-09:00 and 17:00-23:00, say) mean that people could catch you before/after work, resulting in increased business? If this is the case, would it be possible to team up with a local garage that has their own 2/4 post lift, workspace, etc. and do your work when they're not there? Or maybe have an agreement with the place you're at now? On the other hand, do you have your own garage or workshop, or space for one? Is it big enough to take a lift? Could it be? Would the neighbours complain? Would it do for starters? Is it secure? Could it be?
These are just ideas that are flying round my head at the moment, use or dismiss them at your leisure, there's a lot there to consider!