600 is as far as I go,
220 grit is for shaping and getting out deep marks
320 refines the marks of the 220 and is still aggressive enough to do some shaping.
400 is finishing
600 is polishing
new sandpaper is aggressive, but the grit tumbles off the paper and breaks down to a smaller grit as it rolls around on the workpiece.
Use 600 till its worn down and its just like new 1200
dry sanding works but it puts grit in the air so its not good for glasses or cameras or other fine optical equipment so I try to do that outdoors.
wet sanding keeps the grit on the sanding stick better, you only need a drop of water, but I use spit, becasue it has a viscosity that holds the grit on the stick better, water can just cause black gritty droplets to fly about.
being able to accurately spit and hit the sanding stick is a skill

but its handier to apply than water.
Ive mentioned this before, and it got a lot of juvenile reaction, so go ahead, Im used to it.