Hello,
Thanks for this overview.
Unfortunately, it is already not accurate now and will be even less so in a few years; not only because construction prices are steadily rising, but also because land is not getting any cheaper.
It’s true that we are young ...
In my opinion, with your 21 years (such a beautiful age) you are way too planned out; enjoy life! Be curious about the things still to come and don’t limit yourself without good reason ;)
Even if you don’t believe it today, assuming you’ll stay with the same employer/place for life – free yourself from that. My generation already had to change jobs and industries several times, learn anew; this will be even more likely for you and your boyfriend. Who knows, maybe your further education will open doors for you whose existence you don’t even know today?
I also considered the idea of a (cheaper) condominium ....
You should start there if it absolutely has to be property now.
Look at the market and its offerings, attend viewings and if you think you have found a good deal, go through the condominium again with an expert _before_ you even think about signing anything. However, you should first have a conversation with your trusted financer about what you and your boyfriend can shoulder with as little risk as possible.
This way you acquire property and still remain flexible, in case the big wide world calls you. If not, it’s a good cushion for a later new build ;)
Rhenish greetings