There used to be some really good threads that gave step by step instructions in photos in the helpful tips post pinned to the top of this forum, but unfortunately with time and changes to the website the photos aren’t viewable any more. Having said that, the instructions would be virtually that same as they are for cutting the skimmer hole. You certainly can reinforce the area by applying a pool patch if you want to, but I don’t think it is necessary as long as you have the correct gaskets and such - they will provide reinforcement and give a good seal.
Do you already have all your connections and so on? I’m going to attach a couple of photos of my old set up... not sure if they’ll give you the detail you probably need.
So the photo above is the skimmer. Notice that there is only the single pool wall layer. I drained the pool to just below where I wanted to install, installed only the faceplate, made the cut, removed the faceplate and added the butterfly gasket, then installed the skimmer.
This photo shows you the skimmer on the outside, and where I cut the holes so I could add the standard 1.5” connections. Again, I made sure the water was below the openings, and used the gasket/o-ring from the connections to trace where I would cut. Then after I made the cut, I inserted the connection so I could make sure there were no little imperfections in my cut that would interfere with getting a good seal. I installed all the pieces, making sure to use gaskets or o-rings, and used pool lubricant to make sure I got a good seal.
Highly recommend valves everywhere so you can shut off the flow when needed.
By the way, I plugged the one intake since I was using skimmer as an intake. And I replaced the Intex hose with flex PVC.