I can not brush paint.

I find brush painting to be every bit as difficult as air brushing. I use Tamiya exclusively (local availability more so than actual preference, but it does spray beautifully), and find that thinning it for brush painting causes problems. I've always brushed straight out of the bottle.

Tamiya "rolls" up if you try to paint over a recently dried edge, so be patient and allow lots of time between coats.

Every acrylic paint is a little different, due to use of different solvent-binder systems.

The central problem, especially at this time of year, may be relative humidity. For brush painting of acrylic hobby paints, you want the RH as high as you can get it in the winter, usually between 50 and 60 percent, although you may not be able to reach 50%, depending on local conditions. Acrylics dry fast but cure slowly.

I don't have any problems brushing Polly Scale, but you probably need to put on several coats when using a brush. You need to let it cure at least overnight before a recoat, or force cure.

Thinning, or reducing, works well with Tamiya, Gunze, and many craft acrylics, is a good idea, but the amount of thinning is much less than for airbrushing. For Tamiya, I generally decant a small amount of paint, and in another small container I have some 90% isopropyl alcohol in which I have dissolved a small amount of acrylic retarder. (I use this when I spray Tamiya). I dip the brush lightly in the solvent-retarder before I load it with paint, and periodically thereafter. This technique, like all, requires practice. Also works with Gunze.

You can use the same method, but with water instead of alcohol, with Polly Scale, and you may be able to omit the retarder. I don't routinely use Model Master, and I haven't tried Vallejo yet, but similar methods should work—you will have to do the experimenting yourself!

Always paint with a wet edge. Never "pet the paint": attempting to paint over an area you just covered. Recoat later.

Always wait until the paint has cured before recoating. 

For area coverage, use enough brush! The biggest that will fit the surface is the best because the paint on the brush will not dry out so rapidly.

Always mix retarder with solvent, never directly with paint!

My own expereince with those paint brands is that they are from mediocre (Polly Scale/Testors) to terrible (Tamiya/Gunze)to handbrush. Mind you all airbrush well, but they are formulated to perform better that way I believe. The best brand of acrylics that I used to handbrush was old Polly-S. One coat coverage and usually dried without leaving brush marks.

If you work in enamels, I HIGHLY recommend Humbrols!!! Stir them thoroughly and you will get superb results when handbrushed. Especially with some good sable brushes. When I have to handbrush, they are my first choice unless they do not make the color. But I almost always get beter results using Enamels handbrushed over Acrylics.