Any advice on opening a shop?

There are issues with having lots of high end stuff in stock:

1. It's expensive to buy in
   
2. For the items that people actually want you'll be paying more at trade than your customers pay Wiggle at retail
   
3. Combine 1 and 2 and you'll end up being left holding the baby, as it were, with thousands of pounds of stock that you eventually have to sell at a loss - or the receivers will sell for you
   
   

I'd say the stock of parts that you should carry are those that support low effort, high margin, rapid servicing - drop the bike off in the morning and collect in the afternoon type stuff. Punctures, brake pads, chains etc.

If I'm dropping a frame in to have a full groupset and finishing kit fitted then a) I don't mind it taking a few days and b) I'm highly likely to provide the parts alongside the frame.

Honestly I'd run as lean as possible on parts, poor cash flow will kill your new business really, really fast.

Critical thing to focus on, in my view, would be services based stuff - service and experience.

What does that mean? Run me through a bike fit that I can send to Burls, whilst selling me coffee, then get the frame delivered to the workshop along with the parts and build it for me. ~£400 of high margin work that I can't order from Wiggle.

I'd also, as mentioned, focus on eBikes - I personally would like an eCargo bike, if there was a place that I could test one out that was on the way to work I'd probably own one by now. Competition is currently low which likely means that margins are high in comparison to other types of bike.

Aim for a minimum margin of 70% on everything - for a high-staff business, if run lean, that means you can (hope for!) around 20% pre-tax profit (in my experience of FMCG).