Like what Platforms or other means to use and what to look out for?
What should I write ? How much money should I ask for?

I currently mostly do administration of Monitoring Software/Agents but I'm open to doing sysadmin stuff as well.

There are hardly any real freelancers left in Germany because of some weird laws. Better find 2-3 others and create your GmbH where everyone is the boss and everyone has an equal share, then do your own thing as if you were a freelancer.

Get a Steuerberater. IIUC they charge based upon your revenue and it's certainly easier than doing it yourself. They'll generally deal with all the bureaucracy.

Don't use platforms like ODesk/ Fivvver to find work as you'll be competing on price for commodified work. You'll have more interesting and better paid work if you have a hand in developing the role with your clients.

You need to do some sales and marketing work - e.g. create a portfolio and go to events to meet people in the industries you're interested in. Finding work is largely luck but you don't invest the time then you've got no chance.

The fees will really depend on experience and the value you're adding. Check out e.g. Glassdoor for equivalent employed roles to get a ballpark. Estimate 200 days per being available at full utilisation.

Stop right now, nobody needs IT. Find a new branche. Sorry, my dreams were crushed aswell. I am gonna be a facility manager!! :D

(Fucking kill me)

Read up on Scheinselbstständigkeit.
Then talk to a tax advisor that is knowledgeable in that topic.

Only once you fully understood the implications you can proceed - and by understanding I mean realizing how utterly hard the law makes it for regular freelancers.
And don't get me wrong, but if you are unable to understand that topic due to language skills don't do it. Not because it's not possible to understand the legal situation through translating apps - but more because you will get a LOT of paperwork you must understand precisly because one wrong word will ruin you and cost your customers thousands. And which is often required to be send back within days. (Looking at you, DRV)

That being said classical admin work freelancing unlike actual consulting is almost impossible to do under the current laws.

They don't need a GmbH, a UG would do it for less starting capital, BUT a joint stock company does not protect you from Scheinselbstständigkeit per se.

It's a proper clusterfuck.

I'm in German IT for 10 years now, and I'm telling you, don't do it as a freelancer!
The legal framework is so complicated in this space, the overhead makes it unfeasible alone. Out of 20 IT freelancers I knew of in my area, not one is left.

Sadly I concur, every EU country is better in that situation than Germany.

In theory you are right. But with the UG you can't sell shit. Nobody takes you for serious.

The Netherlands isn't. They also punish freelancers.

No longer valid. A shitton of companies are UG by now - I operate one myself. It is very rarely an issue,even back when it's been just an UG we used.