I agree with bish-bash-bosh. Its very hard to make any money on the light stuff. I have tried. I started my own light aircaft maintenance company. If you dont have deep pockets then its hard to keep going. I do some part time work for a GA maint company. They have a monopoly on they airfield that they are based on and lots of work but are still finding it hard.
There are companys out there that do do well. So it can be done. Your 145 approval isnt to difficult to get. But it is expensive. I've seen companys get their approvals where the company management has little to no aviation experience. Its a very expensive process.
Have you read EASA 145 yet?