Hello
sorry about taking so long to reach out to you, but I've been using my own modified aufs package for some time now. I believe it supports all three of your requirements (eg. it creates package aufs-dkms-5.7 for a kernel version, so you can have more of them installed). You can check it out here:
https://salsa.debian.org/jpalecek-guest/aufs-debian
To update to a newer version, do:
$ uscan
$ cd ../aufs-X.XX
$ touch debian/config.in
$ debian/rules files
You can also do "gbp import orig" if you like.
However, there's a more serious problem with aufs. The latest kernel omits the kernel patch needed to make the module, which means the resulting package is useless. See:
What is your take on this? I was using aufs for schroot only, and maybe will try to use other ways.
Regards
Jiri Palecek