It's hard to say with out seeing the car, but I don't need to go to bare metal.

Start off by sorting out all rust, car park dinks ect do this by going round and round the car highlighting every single thing.

Tackle each area panel 1 at a time, once everything is done flat the car with 800 wet and dry. Panel wipe area, then by 2k primer ask at paint shop what they recommend as you can roll/brush this on. It's a bastard to flat down but it's cheap. To flat use 600 wet and dry. Then it's ready for paint. Always best to remove all glass too

Hope this helps mate