I'm in the same boat, I've part assembled my Tau but I fully built my Pathfinders and Fire warriors which was a bad idea.
I'm just starting on the Vior'la scheme, so far all I've done is primed them black and built up to white (I don't know why but to me this looks better than priming white) and started painted some red details.
I tend to paint in a production line and add one colour to all the models at a time then move on to shading later.
The front plates on the Stormsurges are not attached so I can paint the cockpit and crew inside, and I've not glued on the main gun or attached flamers.
There's also some ghostkeels with their leg plating and guns off that need detailing.
Airbrush is a good tool to use
IMO.
Pledge Floor wax cleaner is good for thinning your ink/shade/wash.
If you only use a little super glue when attaching the Tau to their bases you can pop them off easily with a craft knife