What is an appropriate hourly rate for me?

Calculate your hourly rate

Suppose your expenses are annual: € 25,000. You want to be able to cover those anyway.
You would like to make at least € 2,000 net profit per month. Annually, this is € 24,000.

Add income tax and various deductions (about 35%).
So you arrive at a desired gross profit of € 32,400 annually.

With a full-time working week you have 260 working days per year.
Sickness, vacations and public holidays are deducted from this figure.

This gives you about 220 working days, or 1,760 hours (8 hours per day).
Suppose you think you can declare at least half of your hours, then your billable hours are: 880 hours.

Your hourly rate

€ 25.000 + 32.400 = € 57.400. And € 57,400 : 880 hours = € 65.23 per hour.