I use acrylic ceramic paint , bought from Micheals. The stuff is cheap. Thin it with water add a couple of drops of dish detergent to lower the surface tension, and away you go.

I use a filter on the suction tube of my airbrush and this keeps out at "globs" that might escape my eye when mixing.

I always give my tanks a factory finish, and then Dullcoat. This seals the factory finish. Acrylic weathering and washes are then applied. Again I keep preaching this. Windex window cleaner absolutey removes acrylic paint but does not touch Dullcoat. For guys starting out this is important. If you screw up your first attempts at weathering, spray the tank with windex, let it sit for a couple of minutes and then wipe it down with a soft cloth. Your tank we be restored to it's factory finish and you can try again!!!! If you want to lock in the weathering then dullcoat the tank again.

I really think you should stay away from artist's oil paints for a base coat.