To be honest, I don't like the instructions/recommendations at that DIY site. I don't recommend using rough sandpaper on wallboard or you're looking at increasing your work significantly. A light sanding works fine. The show someone setting a nail into wallboard. Don't use a nail for anything. Nails were outdated in the 1800's. Unless you're using one to pick your teeth, avoid them. Use drywall screws for holding power and a head that will properly counter-sink into the drywall and be easy to plaster over without cracking the surface paper.

Large holes need to be reenforced with a piece of wood that's screwed into the wall, not hung with a piece of string. Cut the drywall by scoring it repeatedly with a carpet knife rather than a saw - it will produce much straighter and neater results, making it a lot easier to plaster.

Small repairs, including nail holes or other imperfections need to be "divoted" before they're plastered. That is, they need to be in the form of a depression that rolls smoothly from the good parts of drywall around it. HItting such a spot with the back of the handle of a putty knife usually works well enough. This will prevent your new plaster from forming a bump that you will never be able to smooth out.

On first plaster application, scrape almost all the plaster off. Leaving a lot of plaster is only going to create more work, more mess and waste plaster because it's all going to sand off later. If you're going to need to feather a lot (large areas) invest in a couple of wide knives - 6" and 10 or 12"

The issue I have with the paper edge method as described on that site is that you''re potentially left with a significant bump all the way around your patch which needs a lot of feathering to hide unless you also prep the hole's edges to accommodate the extra paper layer.

Best drywall tips I've ever seen come from the TV shows Holmes on Homes and DisasterDIY, both Canadian shows on HGTV. And of course from watching drywall professionals work on my home. Damn those guys are fast.