I'd hate to start imposing 'rules', so feel free to work on multiple projects
When's the start then?
I've got half a dozen armies waiting and I want to have to decide which, else I'll spend my painting time digging up more and more stuff and trying test paint jobs.
I'm self-imposing a few rules:
(1) has to be a simple paint job and a fast one, as I don't have that much time for painting

(2) has to be one of my bigger forces-in-storage (to help whittle away the mountain).
(3) has to have no irritating or very lenghty jobs (so probably no models with tonnes of flash, or tightly packed bases which are hell to paint or flock; and no models which need hugea amounts of finicky assembly.
(2) will imply that it's one of my GW forces, almost certainly an oldy. In the running at the moment are:
(a) Orks (a somewhat particular force which would include around 50 identical models - now THAT's a challenge! - and a slight twist in the tail)
(b) Epic (6mm) Orks - all vehicles
(c) Epic (6mm) Chaos - with a cunning plan to get away from fiddly basing problems
(d) Epic (6mm) Tyranids as per (c)
(e) Imperial forces hotch-potch (a mix of Pretorian Guard, Kasrkin, SoBs, SMs, Ad Mech - contrary to (a), maximises the mix of models to keep it interesting)
(f) Dwarfs, mercenaries and friends (a bit like (e) in concept)
(g) something else I'll come up with one week after the start.