Debian is Debian. It could work on Ubuntu and similar derivatives of Debian, but due to subtle differences in system design might mess up something.
But yes, just like with Peerbox nowdays - one would be able to install it on server or something.
Yes, I have seen that Nu depends on older and unsupported libdb. This can be solved with “hack” but it is not a long term solution and Nu devs should do something about it.
About updates (indefinite), well that is not so much work. I did say - as long as they are compatible with existing design it should be very simple and not so time consuming. It is basic support, I consider it as an obligation.
It should typically be withing 24h, but if there are some problems with build (like with 2.1 now) it could go up to 72h.
Yes, this is possible. I can maintain both versions in the same repository.
Only me. There is no other way of doing it due to GPG keys. However the binaries themselves can be hosted on official NuBits.com if shareholders agree with that. This would enable webmaster of Nu to deal with them too.