Preparing a car for paint is a tedious
JOB !!!
I know I'm slow, but this is taking forever and a day.
Bossed
Truth there. Key to it is when you get frustrated with a panel (or the whole thing for that matter) is to walk away for awhile and relax. Frustration doesn't lead to a straight panel.
Take a break, have a beer, relax a little. Think over what you're getting done, then go back. So, yes, I mean for you to literally to get physically away from the vehicle. Trust me on this one.
Also, focus on each area you are working on. Stop thinking about the whole job, it gets overwhelming when you consider the whole thing. Take the left fender and make it the best you can. Go to the right fender next, use what you learned from the left one on it, and so on and so on....
Keep in mind that when you are finished with a panel, you can forget about it. Also don't forget there are only two fenders, only two bumpers only two doors, etc.. You don't have to fix a hundred of each, just those two and you're done.
Keeping your mind fresh is so incredibly important when you want your mustang to turn out nice. Frustration and worrying about time will make for bad bodywork, bad paint, etc. It'll take how ever long it takes. I spent a year on my red car on bodywork, plus more for smoothing, mini-tubbing and other improvements.
Don't get a firm schedule in your head, this isn't an HCI swap that you can have done in a couple weeks.