I think having a selection of parts in stock and on display is much more important than having lots of bikes on display around the shop. A few of my local bike shops are over half full with complete bikes, none of which are under a grand. I'd not buy a complete bike for that sort of price, much prefer to pick the frame I want and then either buy the parts to build it myself or get the shop to put it together. But once the shop is mostly full of bikes there is limited space for other parts so they only have small tyre sections, no brake sections, bike lights, bars, headsets etc... As a result I'd not buy much from them so wouldn't go to them for a custom build.
Communication is vital for me also. I don't want to have to go into the shop everytime I want something or to discuss a service. So if you offer a telephone number you must answer it reliably. Also with email addresses you must reply by the next day. If you don't then for me I'd not order anything with you as I see keeping in touch would be difficult. I was trying to buy a black santa cruz chameleon frame a year ago, I searched on-line for shops that stocked Santa cruz. I emailed them, many just didn't bother replying, some tried to convince me I wanted a different size frame because they didn't have, and couldn't get, a black medium frame. Some emailed back once and then couldn't be bothered to continue responding to my questions. Others just didn't answer their phone, and some that did said they would call back once they checked their stock and then never did. I ended up buying from Leisure Lakes as they were very organised, friendly and attentive to my needs. I had the frame within 24Hrs. So if you want people to cough out over £1000 on a custom build you need to have excellent communication lines set-up.