I use Master\'s Touch primer for metal minis. It sticks well, doesn\'t go on too thick and I seem to have less problems with it overall than with Krylon. Can get it at most Home Depot stores. Can find it at smaller chains too--I usually get mine at either Menards or Do It Best.
For sealer I use 1 coat of Krylon Crystal Clear, then 2 coats of Testors Dullcote over that. I quit using Krylon matte spray when they decided to start changing the formula every 6 months or so. Half the time the \'new\' formula would dry to a dusty looking finish and ruin whatever I had sealed with it. Don\'t mind it so much for pieces my husband is going to play with, but sucks to spend hours on something to sell and have it ruined in 30 seconds.