My questions regard, what regulations are there for foreigners who do self-employed business using European equipment in Thailand.

Products are not sold in that kind of business. It's a service job using the equipment of the company. The company is responsible for promotion and it is also not a franchise. In Europe this could be a second job for people who don't earn enough in their first job.

My questions:

1. Is it necessary to register a company to do that kind of business?

2. I have a work permit, is it possible to obtain a second permission for a job?

3. How would the income be taxed?

4. Can foreigners do that kind of service occupation?

5. Can I work as a self-employed worker here?

Any suggestions? Thanks

... what regulations are there for foreigners who do self-employed business ... in Thailand.

The one and only regulation I've heard of is: "Not permitted"... Meaning, that you need to be properly employed by a proper employer - such as e.g. a company formed buy you - in order to work legally in Thailand.

This should answer your questions 1) and 5).

As for question 2) and 3) - yes, you can have more than one job and more than one WP and you'll pay regular income tax of your salary.

As for question 4). What do you mean by "that kind of service occupation". If what you have in mind, can be done by a Thai - it would be very unlikely a foreigner could get a WP.

The Bottom line is - how profitable this service business of yours expected to be.

If you expect a modest income, the overhead of running a company will take a significant % of it and will very likely make it not worth while.

At least one of the following - 1. Profit margins, 2. Turnover - should be pretty large to justify a company.