If you have a vinyl top then remove the molding separating the vinyl and paint. Drip rail chrome really should be removed also, but can be extremely hard to take off undamaged. If you plan on buying all new drip molding then definitely remove the old for painting. But if you want to keep the originals then it might be better to leave them on and let the painter mask around. If you have hub caps it's easy to just take them off. While the paint shop should completely mask all four tires, overspray can still find its way in. It's sometimes better to play it safe and just remove wheel covers.
The paints may be applied by brush or spray; the small spray attachment for vacuum cleaners is very convenient, especially for painting radiators.
Basically what you're looking for is a good, solid foundation of existing paint that is stable and still strongly bonded to the car. Many times an original factory paint job, even after decades will meet these criteria.
Cheaper then doing it yourself. Some would argue that if you're going to all the trouble to fully prep the car yourself, then why not just shoot the paint as well? Why get a shop involved? The answer is simply that you'll get a better job and for less money. Some would argue with this, but the fact is that if you've never sprayed a car before then your first car will have a steep, and expensive learning curve. Laying down an even, consistent coat of paint takes considerable practice. Also, paint and equipment is not cheap. You'll need to buy primer, color coat, clear coat, reducers & catalysts. None of these are inexpensive and you can easily spend as much in paint materials alone as the cheapest paint job at Maaco or similar shop.
By far, the most important characteristic in determining whether you are Warm or Cool is your hair color. If you can't determine your exact eye or skin tone, then your hair color will provide the answer. Why? It frames your face!
Masonry paints come in a wide variety of finishes, from textured to ultra-smooth. Opt for a texture if you need to disguise fine surface cracks. If you favour traditional finishes, then consider limewash, which is available from specialists such as Francesca's Lime Wash. The beauty of this paint is that it will mellow and weather with time. However, do check with the supplier first to ensure that the surface is suitable for this finish.
At a minimum you want to remove all the chrome from the car. Take off both front and rear bumpers. If your Mustang has bumperettes that are body color be sure to bring them along so they can get sprayed at the same time as the rest of the car. Remove all rocker, hood and trunk molding. Same for wheel well molding and all emblems. This would be a good time to order some new emblems and attachment hardware. Also spend some time cleaning up all the chrome with #0000 steel wool. Nothing looks worse on a fresh paint job then faded emblems and corroded, cloudy chrome.