40K Sponge painting on large panels

I need help with some painting tips.

My warlord titan arrives tomorrow so will be a while before painting begins as pinning and magnetising the the big fella.

I don’t own nor want to own an airbrush at this moment in time

Just need general help with painting tips for it as the panels are massive compared to and of my 14000 points of ultramarines.

Any help will be appreciated 😁