I develop emulsion side up, and I'd say start with three or four sheets before trying more.
Make sure you've got enough solution in the tray.
Insert the sheets with a sweeping motion from the front of the tray to the back, slightly lifting up on the leading edge, so that it doesn't scratch the next sheet, and pat down with your fingertips. There are good illustrations of this in Adams' _The Negative_.
Surgical gloves not only protect your hands from the chemicals, but also protect the emulsion from your fingernails.
When pulling from the bottom of the stack, be sure to pull straight out, so that the corner of the second sheet from the bottom doesn't scrape the sheet you are pulling.
If you're using one of the more fragile East European films, you may find tray development unsuitable. Even if you refine your technique, you'll still get little abrasions, which may or may not show up in the print. Alternatives are tanks and hangers (good for high volume), drums (not all developers work with drums), and single sheet development or brush development in trays.