If you can download and then unzip a file, you can run this. That's all that's needed. It's just over 3 gig and when unzipped, takes up about 8.5 Gb of space. As with any mega mod, system spec is a bit higher but mine is quite dated and it runs just fine. Won't hurt to try!
Installing the included SH3 Commander utility is easy but entirely optional.
As is using Mullti SH3 - all it does is tell one of your installs to put its career and other savegame files in a separate folder. AFAIK the only harm NOT doing that will cause, is that if you load a career file from one install into a different one, then it likely won't play, so you have to remember which careers belong to which installs.
Existing careers from a different install won't work with this, you would have to start fresh ones, but well worth it.
Just download the latest version of GWX OneAlex Edition from the link on that Youtube video, and open it with 7Zip or similar. Then use 7Zip to extract it (it's a folder called SH3) to somewhere outside C:\Program Files (x86) and not to the same folder as your existing install - it is a completely separate install that will leave your existing one alone, not something you install or enable over the top of it - don't do that!
SH3 is great out of the box but a mega mod will greatly improve look and gameplay, and this new one looks like one of the very best, and is very easy to get up and running.