The archive will probably take several months before it's up, and maybe a year to have all the features implemented. Expect it to be properly usable about four months after it's up; the custom level forum will probably be deleted, so nobody will be able to properly comment on levels for that time.
(I am not LPChip, Paula, or anyone else who would know anything about this archive specifically; I speak from experience.)
As far as tilesets go, just post them in Development Showcase. It isn't as though that forum is clogged, or that it will become clogged, because making a tileset actually requires a tiny bit of effort and thus we don't have the slew of crap that torments the custom level forum and especially the archive.
However, posting "suggestion: add a tileset board" topics every week is a good way to tick off Paula. Expect a sarcastic and slightly scathing comment as well as a lock.