What should a sanded surface look like between coats? I am using an oil based paint on some flush panel doors.
I am using a Wagner spray gun. I have already applied my first coat.
I intend on using a 240 grit sand paper after the first coat and and finishing with 320 grit sand paper in prep for my last coat.
When I look across the surface should it look completely flat or should I see little stipples / bumps?
Wagner makes several spray guns. Some adequate for your job and some not. The hand held self-contained guns will not produce as smooth a finish as will the unit which pulls paint out of the paint can and pushes it through a hose and gun. Reason for this is the pump will assist in atomizing the paint and will help the self-leveling characteristics of the coating.
You are ahead of us in expecting a smooth finish if you are using 240 and 320 grit paper. The highest we normally use is 180 grit paper.
Another concern is the lack of mention of using a primer. If no primer was used, you will not achieve as smooth a finish as with one. Multiple coats will help reduce the little bumps as they are generally a result of raising the grain of the wood. The most difficult smooth cabinet door finish to achieve is one applied to a "Manufactured" wood door, also known as a composite wood.