If the paint is peeling you really should strip it all off. Your outer coat will only be as good as what is underneath. Sealers and epoxy primers work great but any delaminateing paint will bite you down the road if not removed. I don't know if the car will be stored inside or out, but if it is out for any long period of time I would coat any bare metal or fresh filler surfaces with a epoxy primer to prevent rust through. Most primers are porous and will let water seep through and rust if in moisture for any long period. Epoxy will not.If the car is going to be inside then bare metal can be treated with a etch primer followed by what ever you choose.Check your local auto paint supplier, and they can help you with what brands that are cheaper. Be carefull though, because when it comes to most paints the "you get what you pay for" saying does apply. Though I have heard of people using cheaper products and having good luck. It is your car and your choice as to what route you go. Just remember body work can be time consuming, but rewarding when done right, but not at all fun if you have to redo because of a product failure. Just my 2 cents. Good luck
Bob