Sometimes ya just can’t airbrush everything. You have to brush stuff by hand. Especially small bits. I have a variety of brushes that I’ve purchased from hobby shops over the years. I also got some nice artists oil brushes from my daughter this last Christmas (thanks Tiff). If you want to pay more – buy brushes from a hobby shop. You can get better prices at places like Michaels caft stores. I keep my brushes in a block of oak that I drilled several holes in. That works better than putting them in a jar. It’s easier to see the individual brushes. You should clean your brush a soon as you are finished using it if you want it to last. Once the paint dries on the brush it’s toast. I have plastic tubes over most of my smaller bushes – that keeps the points safe and they keep their shape better.
I find that at my age I usually need a magnifying headset when I paint the small stuff – that can make a real difference. Good lighting is a must also. Here is a pic of the magnifying headset (Donegan DA-4 OptiVISOR Headband Magnifier, 2X Magnification) I use.