How is the package situation on NixOS nowadays? Do you find you have to custom install a lot of software or are there native Nix packages for most everything you need?
What kind of learning curve should one expect if migrating from debian/ubuntu based distributions?
There are existing packages in Nixpkgs for almost everything. Home-manager has firmly emerged as the "configuration per user" tool. I might say, in fact, get comfortable with home-manager and then switch to NixOS, if cold turkey sounds like a lot.
Its a very, very different sort of distro, but if you know basic function programming and are willing to do some "unlearning", you should be fine.
What kind of learning curve should one expect if migrating from debian/ubuntu based distributions?