Like someone said, it's mostly application.
I dont consider myself a pro or anything, but ive been doing body and paint for a good 5 years along with running my own shop with paint booth and all.
Flats are nice, I am actually considering it down the road for my mark. But this means ridding of all the shiny stuff to accommodate the look.
If you havn't already, you should consider HOT ROD FLAtz. They have an array of flat colors to choose from.
http://www.tcpglobal.com/kustomshop/ksflatz.aspx
Owning a Mark, I have to say.. It's a big car. Labor will get the best of your money.
-Sanding down
-Fixing Body imperfections (dings, deep scratches, etc)
-Primer
-Final coats
-My favorite in all this, Masking- Even more fun if you want the door/drunk jambs, under hood/trunk lid done. Which comes before Spraying of course.
With just the exteriors Good painters will get away with 1.5 quarts of Base-Coat paint (urethane). That's good for 2 good coats. I'd say 2.5 quarts of ClearCoat (with Flattener and catalyst), for a good 2-3 passes.
If you go with a Single stage paint, like the HotRod Flatz.. Stick to the CLearCoat guide above +.5 You're better of with buying their gallon.
If you were to bring it to me, exterior only. I'd say 1500, with no body work.. and 2k+ with. That would be your standard paint, not hot rod flatz. They're a bit pricier than you're everyday PPG and Dupont.
I've seen Vintage car done up with HotRod Flatz.... looks sweeet.
Good luck!