If it's over 40,there will be hidden rust you'll find once you remove paint.If it's always been a Fla. car of course it won't be anything like what we find here in Ohio but what I would suggest is that if the rust is extensive and you are not experienced with fillers then you may want to consider replaceing certain panels if you see that you will have major rust repair.Depending on the make/model of the vehicle the replacement panels may not be as expensive as you think.
I've seen that paint on e-bay but I've never used it.