An older gentlemen in Canada has this website where he describes brush painting a frame in detail.
I came across that site too and had a good read before I painted my frame.
What I found was:
Don't try and apply paint too thick. Apply several thin coats, three in my case.
Allow plenty of time between coats for the paint to harden, I left the frame and forks on a radiator for four or five days between coats then rubbed down with fine 1200 grade wet and dry before applying a subsequent coat.
I left the final coat for a good week, before buffing with some T-Cut, then applying some wax polish.
Try to work quickly and don't fuss too much. If I you get a run, don't worry, you can flatten it out with some wet and dry before applying the next coat.
In the end it wasn't that much cheaper than powder coating. I had a frame shot blasted and powder coated for £40.00, but I had to courier it to and from a place 200 miles away, which cost an additional £30.00. The paint, a decent brush and a few sheets of wet and dry cost me nearly £30.00, plus a good few hours of my time. If there was a decent, fairly cheap powder coater nearby, I'd probably have had it powder coated.