Thank you very much for your replies! I'll try each of your suggestions over the following days and will report back.
Aaah, you're right! I thought that doing define in a begin-for-syntax was exactly doing define-syntax in begin-for-syntax, but I now see that I was wrong. It is even obvious now that you helped me state my confusion 
No, and it looks interesting! I'll try it out, first and foremost to learn more about Racket macros.
Oh, I thought about syntax classes, but I had the impression that they were an overkill for my needs. Now that you evoke them, I realize that they may quite relevant.
I was indeed looking at quasi-syntax and splicing quasi-syntax, but I couldn't figure out how to arrange the whole thing. Thanks a lot for providing a code example, it's very helpful!