A small piece of gratuitous advice, ingore at will!
If there's no maintenance company at an airfield there's probably a reason, such as not enough business to sustain one. Perhaps one started and failed in the past..beware.
Your market is based owners to a small extent, drop-in visitors to an even smaller extent, and business you can suck in from the UK to a much larger extent.
Consider the opportunities offered from up-coming legislation, CAMO etc. The GA maintenance industry is, as a generalisation, so luddite and conservative that anyone with imagination and flair can steal business from under the noses of the established maintenance companies while they delude themselves that nothing has changed.
Being honest, really honest, with owners is a good start. Minimising costs instead of maximising them; not doing unnecessary work or replacing components that don't need it. Sticking to your estimates would set you apart (That means getting them right, of course. It's not impossible). I'm not an engineer but I have run an M3 business in the fairly recent past. All these things worked, although the engineers in the company thought that it was the end of the world to tell an owner what the work would cost before doing it, rather than afterwards.
I'm out of that now....so Good Luck. And...don't worry too much about being on the same airport as another company. Just take their business away from them. Go for it aggressively; beat them on price, quality, service and marketing. Forget about a big car and a fat salary for a while. And remember that they are there because their customers are based there, or like going there, in sufficient quantities to make the business pay.
Above all, do quality work at fair prices, and fulfil your promises.