It doesn't matter if you already have a full time job or not.
Yes, you can do the Nebengewerbe/Einzelunternehmen while having a full time job. You should create an additional bank account and use that one for your side business, which will make it easier for book keeping (otherwise you have to open your private bank account to the tax authorities). You can also get a VAT ID, if you do EU business outside of Germany.
Freelancer is something else as you might think, some jobs fall in the category of "Freiberufler", which is some creative jobs, etc... All others are simply "Gewerbetreibende".
You can also found a UG/GmbH on the side, you don't need to do it fulltime. You should look in your contract though if there is anything that prevents you from doing so.
Sadly I can't suggest anyone since I had to take care of everything myself as well, I simply work together with a regular tax guy. I am based in Germany as well and started basically the same way as you.
> It doesn't matter if you already have a full time job or not.
It does, assuming he's going to have his company pay himself a salary. (Otherwise he'd need to wait for the yearly dividend.) In case of a salary, he'd have to
1) pay for social security and so on and make arrangements with his employer (basically, to decide who pays how much).
2) again, make arrangements with his employer because of the non-compete rule. It doesn't actually matter whether it's mentioned anywhere in the contract, as it's the law. (I forgot the exact article but it's somewhere in BGB.)
It matters a little but not as much as you may think.
(By the way nothing says the dividend has to be yearly, as a company you can pay multiple dividends a year if you so choose. It's more paperwork, and probably costs more in time from his accountant but otherwise you can do it as far as I know.)
Onto the two points,
1) The Social security is based on their wage, and no arrangement with the employers bookkeeping is needed. Their full time job would likely be Tax Class 1 (Or 3 if married) and the second job would be Tax Class 6. If there did happen to be a discrepancy it would likely be small, and paid back when they do their tax return. I also think that the Geschäftsführer of a company doesn't pay social security (or maybe pays a reduced amount?), but I might be wrong on that bit.
2) Yeah he/she must inform their boss, but unless they directly compete with the company, or the side business would affect their job performance they don't really have a valid reason to say no.
My suggestion would be to form a UG, they're relatively cheap and would be easier than the hassle of a foreign company. A foreign company whose operations are based completely within Germany would be liable to pay tax in Germany anyway.
I've heard http://firma.de are good with this sort of thing, and they have several articles on the different company forms in Germany to help. I am however in no way affiliated with them, and haven't used them myself yet.
Yes, you can do the Nebengewerbe/Einzelunternehmen while having a full time job. You should create an additional bank account and use that one for your side business, which will make it easier for book keeping (otherwise you have to open your private bank account to the tax authorities). You can also get a VAT ID, if you do EU business outside of Germany.
Freelancer is something else as you might think, some jobs fall in the category of "Freiberufler", which is some creative jobs, etc... All others are simply "Gewerbetreibende".
You can also found a UG/GmbH on the side, you don't need to do it fulltime. You should look in your contract though if there is anything that prevents you from doing so.
Sadly I can't suggest anyone since I had to take care of everything myself as well, I simply work together with a regular tax guy. I am based in Germany as well and started basically the same way as you.