I only go to about 100 grit for anything that I'm not intending to sell. The 400 grit school may be fine for competition, but not with a plane like you describe.

I use fine sanding block (the foam rubber covered with grit kind) and just wipe over the model with it. Then I run my hand over it to feel for mismatches of sheeting, then vaccume it and wipe it with a tack cloth.

When I did silk and dope, I went down to 320 grit before final coat, but that was more or less to knock off any fibers before I put on the paper and silk.