Hello Till!
Well, I hope I can make this clear. Just ask me whatever still confuses you after I do my best to explain.
First, the "sixpack" is called "abs". Yes, so when we say "abs", that's what we mean. And yes, you still have to train your abs. Just do weighted crunches, that'll be fine. What's more critical though is the diet.
Yes, you can train everyday, but only if you don't use the same muscle group. For example, I can workout my chest on monday, then my legs on tuesday. That's ok. But if you do a full-body workout, then you have to wait for at least 36 hours before you can train again. This is because the muscle needs to recover first, and 36-48 hours is sufficient.
If you have to start over again because you want to correct mistakes in your training methods, find your maxes (if you haven't found them yet) then do strategic deconditioning (or SD for short, which is simply intentional rest for most purposes) for 9-12 days. If I were you, just schedule your SD to end on the Monday that is nearest to 9-12 days. For example, if the 11th day of your SD is Monday, then stop your SD on the 11th day and start working out again.
If you don't have enough weight (referring to weight plates, the load, or the "Hantelscheiben" as you said), you really have no other option but to buy more of them, or join a gym. Of course, if that's not possible right now, then in the meantime, while waiting for the possibility to arrive, simply do the exercises that you can with the limited weights that you have. For example, if you only have a total of 60 kg of weight available, then i'm sure you can still train your arms and finish one whole cycle with that weight. Also train your chest and other large muscle groups until you reach your maximum available weight (60kg in this example.) After that, continue with your max weight for two more weeks, then if the cycle is still not over because you still have to train your smaller muscle groups, just drop the exercises that require more weight.
I hope that helped. I'm sorry but I really can't speak German.
Good luck!
-JV