You can paint over eachother with no problem. I don't even us a clear coat between them.
But if you us oils over enamal, you need a clear coat.
If you have trouble handpainting Tamiya paints, mix 1 part Future and 4 parts distilled water. Then dip your drush into this mixure before dipping it into the paint. This acts as a flow improver.
Also you can get a slow-drying blending acrylic medium and mix in with the paint to give you a lot longer drying time. This really helps with brushpainting since it won't dry on your brush so fast.