Here's how it goes with War Walkers in the Baast Warhost: You gotta paint everything separately. I've painted the legs separately from the cab, as you can see below:
I even built little stands out of soda bottle lids so I could prime and paint the "ears" of the War Walkers.
Before long all three will be built, but it's a slow process that's fussy. I just keep telling myself that I'll be so glad I took all this extra time when they're done.
Speaking of all that fussy still I'll be glad I did when I'm done, the Vypers are a good chunk of the way there. As you can see, the assembly is mostly done, but there's painting and inking still to be done.
War Walkers and Vypers are the most fussy models in the Eldar line because you gotta assemble and paint in stages, whereas you can just slap other models together and then paint without having to think about what comes first, what comes second, etc. Due to the fact that I'm sort of bad at this kind of organization, I play it extra carefully and move very slowly.
I'll be glad when these are done. Seriously.