I am a UK ACMT qualified technician working for an AASP, and have been qualified in different guises since 1990. Previously at my last employer, an Apple Reseller, I dealt with their application to become an AASP.
Being ACMT qualified doesn't permit you to obtain Apple parts, use GSX or claim to be authorised by Apple to undertake repairs. It is the AASP (Apple Authorised Service Provider) that is authorised, not the technician. Your ACMT status only allows you to work on Apple kit at an AASP or ARS. Even then, to handle most new products you have to complete further on-line training as required. You can obtain the information on how to become an AASP from Apple. Last time I went through this process you had to have business premises, you can't operate from home. I believe the requirement is more stringent now, Apple requiring you to have a high street presence. Signage has to be in line with Apple's spec. The premises will need to have a reception/waiting area, separate workshop and secure storage, plus the usual security, health and safety, insurances and test equipment. Jigs and fixtures have to be bought from Apple. Work, training and other procedures should be in place. Investment will be required for Macintosh computers, displays, Macs for admin, a laser printer/s. Apple will also want to audit your last accounts and you will need to be VAT registered. Parts ordered from Apple are invoiced and the payment taken via DD. Customers complete surveys reporting on their repair experience, and an Apple representative visits you annually. Apple run a tight ship.
You mentioned you undertake some Apple work at a workshop. Providing they meet Apples requirements, could you persuade them to become an AASP and give you employment? You could also seek employment at an AASP. Currently the Apple stores are getting busier with longer delays for appointments, and they are referring more customers to AASP's. If this continues and the AASP's don't have spare capacity there might be openings there.
If you want to undertake repairs on the kitchen table you are on your own. Remember most newer Apple kit uses Apple proprietary parts, no memory or standard hard drives you can replace (other than in the Mid 2012 13" MacBook Pro). During and after a repair Apple proprietary software is required to conduct diagnostics. Additionally for some newer products the keyboard mapper software needs to be run, you won't have access to any of this software. A few businesses break Mac's for spares or do dodgy deals with AASP's to obtain spares to sell. They charge more than Apple would to an AASP, so your repair would be uncompetitive against an AASP or ARS repair. If you fit a part from such a source then find there are additional problems you are on your own.
Hopefully this will partly answer your question.
