How much reserve in addition to equity?

If I were single, I wouldn't worry at all about a cushion. Carpe Diem. Now I have a family and their need for security is structured differently, and I don't want to be a burden to the boys later on.

It is, as always, a matter of type.. Various aspects have been asked and mentioned here. All of them show, in my opinion, an increased need for financial security.

The classic recommendation has already been mentioned, setting aside 3 net salaries. Ultimately, the high monthly savings rate clearly shows your actual monthly financial needs. The rule of thumb is based on an average, and that has a savings rate of around 10%. You have 30-50%. So there is already a lot of additional leeway.
Of course, it could also be 5 salaries, but it is certainly not really necessary to reserve a whole €20,000 for that. Half of that would be okay at that age and in that profession. The fallback option with the parents would even allow for more risk.

The same applies to retirement provision - of course you can save for both a condominium AND retirement. But if there is already a company option with 25% of the monthly net being saved, the third, personal investment pillar does not have to be funded on the same scale - €200, for example, in ETFs is fine. It can be adjusted later and if needed. You have a pretty luxurious starting position here if this company component is secure and not tied to any minimum periods so that you cannot lose it.

What I find more interesting here is the question of whether one really wants to buy a condominium in this phase of life AND this phase of the real estate cycle. Ten years ago, this would certainly have been financially interesting. But today, they are no longer bargains.
If, in your mid to late 30s, you perhaps have reoriented yourself professionally (which is not uncommon in the consulting sector) or also in terms of relationships, it might be better and provide more security to have a large amount of equity with which you can then act flexibly.

If buying instead of renting is really the issue - in principle, it would certainly be feasible to already invest the €100,000 equity now if something suitable is found. Saving for two more years (~€50,000) would also be offset by rental costs of €18,000. And if the market continues to heat up, purchasing costs could also increase by 10%, which would completely negate the savings effort.

If you then possibly reorient yourself in your mid to late 30s, professionally (which is not uncommon in the consulting field) or also in terms of relationships, it might be better and provide more security to have a large amount of equity that you can then act flexibly with.

I have been employed in-house in a relatively stable industry in my dream position for a year, which is probably also why I am "settled down." If something should change in terms of relationships (rather unlikely), I would likely sell the apartment in the medium term and use the proceeds to co-finance the construction of a house.

Saving for two more years (~50,000€) is also offset by rental costs of 18,000€. And if the market continues to heat up, purchase prices could also increase by 10%, which would completely negate the savings effort.

That is also my concern, so I monitor the market regularly; however, I am not yet in the mood to buy. I think it is time for an appointment with a bank to outline the financial framework.

I have saved about 100k equity + 20k emergency fund so far. About 20k of that is in ETFs, the rest is in overnight money accounts. If everything goes smoothly, I should have reached 150k by 2022. Finding the right apartment will probably take another year.

I am in a comparable situation - 32, married, and 4.7k net (my wife is currently not working). For the amounts you mentioned, I have just purchased a terraced house as a new build - final price around €550,000 with an equity investment of 100,000. If a new build is an option for you, you can continue to save money for the own work until moving in. For example, at €2,000 monthly for one year, that’s another 24,000. Before Corona, there were interest rates of under 1% for 20 years, for example.

I am in a comparable situation - 32, married and 4.7 net (my wife is currently not working). For the amounts you mentioned, I have just purchased a newly built mid-terrace house - final price approx. €550,000 with an equity contribution of €100,000. If a new build is an option for you, you can also continue to save money for the labor costs until moving in. For example, at €2,000 per month, that is another €24,000 over one year. Before Corona, there were interest rates of under 1% for 20 years, for example.

My goodness...

Unfortunately, you have to pay here in the Rhein Main area if you want to have your own four walls. For condominiums, prices of 350,000 to 450,000€ are sometimes called for - but that is a topic for another time.