I see that you are in the UK, so maybe parts of this will not be the same, but keeping that in mind, lets proceed.
Processing films: Kodak reports a 10% decrease in film sales per year.

In my experiance, most folks want their film developed at the lowest possible price, can she compete with the big boys with all their very expensive equipment? That equipment allows one to do a great many rolls/hour or day, but if you buy/lease the stuff then you HAVE to run a great number of rolls in order to make the payments.
We were offered a mini-lab and the saleman said something about only needing to do 4 36 exposure rolls a day to pay for it. When you do the math, 6 days/week times 4 rolls = 24 rolls per week. But the average amateur shoots maybe 1 roll per month so there fore you need 96 active amateur's in your community that will without fail do a roll of 36 every month. When I was at another place watching their machine in action, I saw a roll of film that had 3 Christmas's on it, all shot in the same room, all with different trees and with all the kids getting bigger and bigger in each of the 3 different series. So much for a roll per month!
Selling cameras: We found that we could not buy (at a wholesale cost) cameras at a price lower than the big boys were retailing them for. The reason was that we wanted to buy just a few of each model, while they were buying them by the truck load.
We did have a darkroom and did some very custom (meaning all hand done and very expensive) film processing and printing. We also did some of the stuff we shot in our studio etc. However all those folks who brought us film to do got interested in going to digital so they could do it themselves. So we finally closed the darkroom, put the equipment in boxes and now have that room full of computers so we to can do it digitaly!
I hope that this does not sound all negative, but I really do not see any future in what you describe. However if you do decide to try it out, please look into all the details.
Wishing you well, Mike