DOT 4 has a higher boiling temp than DOT3, which means it will withstand higher brake temperatures. 4 is also less likely to attracting moisture - more important to cars that aren't used for extended periods. It also costs a bit more so if you're a driver who is not too hard on the brakes and drives fairly easy, 3 might be sufficient.
Yes, there is a specific procedure and sequence to bleeding your brakes. Most Hanynes manuals outline the procedure for specific models well.