Hi Richard, welcome to UKAT.

I'm not sure that qualifications are your top priority. Have a look a the various posts on this forum and judge for yourself whether you think you have the knowledge, skills, and equipment to cope with modern vehicles. You might find it easiest to do the simple stuff yourself and farm out the more technical bits to someone more established.

Bear in mind that on an ever increasing number of cars you will need diagnostic equipment to fit batteries or brake pads amongst other things - as well as resetting service indicator lamps.

For technical data most of us use Autodata - essential if not perfect.

In terms of general advice, I'll offer the same as I give everyone else starting up - whatever their business:

Get a good accountant.

Make sure you have the proper insurances in place - before you need it.

Join the Federation of Small Business - excellent advice and backup.

Finally, Good Luck, I think you're gonna need it.

Dick