From memory, I have just over 9k of Eldar painted (but don't expect anything special, I'm a crap painter). The models I have go something like
this.
At a rough glance it might divide up into reasonable 3k armies, if not tournament-competitive ones. I do have more Eldar I can paint - next planned is a Warlock which I could try to get done. That will take it to 10k and make it easier to make 3 x 3k.
I don't have any 'nids though, so if it's going to be nids v imperium I would prefer to focus all my painting time on getting my new Steel Legion up to 3k. Basically it's better for me if I know in advance.