brush questions

Secret to brush painting, as with so many modeling skills, is practice, practice, practice.  Indeed, WW1 aircraft is a good place for hand brushing, as are ships.  Also, you need to rest part of your hand on some part of the model.  Just keep out of wet paint :-)  The closer you can rest a finger or whatever to the area you are painting, the better you can do fine lines and detail.

Go to a Michaels craft store or an art supply store.  Overwhelming selection of brushes available.  I find at craft stores the brushes in the craft section tend to be a bit cheaper than those in fine arts (oil painting) section.

You need some high quality brushes, no substitute. I've had good luck with Gunze's brands, Testor's Model master range (not the crappy Testor's white handled ones), and Zuki Mura also makes excellent brushes. I think all these are available at Sprue Brothers.