I am not saying don't go for it all I am saying is do your homework first.
Working with a Bulgarian will certainly help with the red tape but they may be a down side, many Bulgarians have different business and work ethics to western europeans.
I have heard so many times "I do not want to make a fortune just a small living" it does not work like that...for the average western european living in bulgaria he has to make a fortune in bulgarian eyes just to live.
If you get it right you will succeed and I hope you do.
Again I think it would be a mistake to concentrate on brits because I do not know think there is any area in Bulgaria where the population would be high enough out of the hundred or so brits I know in my area only four have bothered to get their vehicles converted, you would possibly make more money in tyre repair and straightening wheels.
As I say I am not trying to put you off its just that I have seen so many try and fail with different business start ups. What you are trying to do is set up a business doing something you can do well.Management skills are more important than just working on the spanners, just look at the fate of the rover car plant in varna and the demise of rover in the uk, the closure of the varna plant was certainly down to management skills and a large part of the uk demise was down to management.
I realise my posts are not very positive and I do wish you well just as I wish the Bulgarians who go to the uk well after I have told them the streets are not paved with gold.
Do plenty of research, chose your partners and bulgarian advisors well dont rush into anything and above all enjoy yourself.