Advice: Looking to start a retail shop in the UK

[focussed]

I'm looking to open a small computer retail shop 'somewhere' in the UK in the next month or two. This is a new venture for me, so I'm looking for someone who is already established, and can spare a moment of their time to offer some tried & tested advice.

I have over 15 years PC experience troubleshooting a wide variety of hardware & software problems, and it's about time I put my skills to making money for myself instead of for other people.

I'd be interested to know if there is a forum dedicated to UK resellers, as I'd be on it like a rocket.

The kind of questions I need answers to are:

Where do you send printers to be repaired, if you can't repair them yourself?
What software do you use to log in repair jobs and print invoices?
What methods have you found most successful to market your business?
Where can I obtain POS product advertising materials?
I have access to many Uk trade suppliers, but which ones are the best?
What kind of hardware, and software markup do you add?
What hourly rate do you charge for repairs?
Should I order pre-built PC systems, or buy-to-build from parts?

Please don't reposond if you don't have a shop already; it would be nice to hear from somebody who really knows what they are talking about here. Worldwide shop owners opinions also welcome.

Thanks for taking the time to read this.