I just completed it recently, with two full playthroughs
The way I engage with every Pokemon is basically the same, dating back to the original generation.
I’ll finish an initial run with my game of choice (anything that resembles the color red is usually where I drift toward, going back to my original choice of Pokemon Red) and get every single Pokemon possible, then buy a copy of the other version. I’ll scour that, and transfer all of the exclusives back to the original version. I managed to finish that whole process (amid a ton of other work in this busy year!) recently, and wanted to check in with the community and see where they were at. Or if y’all even care!
It was fully organic, with some transfer help
Since I completed my quest across two games on one Switch, I needed a little help. My wife, who is working her way through Violet, thankfully assisted in swapping over some of the evolution-through-trading Pokemon, as well as transferring all the exclusives I caught from Violet back into my “main” Scarlet file.
As a reminder, you’ll get the Shiny Charm for your efforts if you speak to Jacq in the biology classroom after completing the Paldea Pokedex. The 400th-catch reward in your actual Pokedex is a Beast Ball. My absolute last 400/400 Pokemon for the Scarlet & Violet generation was Iron Thorns.
Weirdly enough, the last Pokemon I needed for my generation 1 ‘Dex was Tauros. I did everything else, and never managed to get one from the Safari Zone on either playthrough: so I grinded it out last.
You can also wait for the spring Pokemon Home update
In “spring 2023,” (knock on wood) Pokemon Home functionality will be coming to Scarlet & Violet. At that point, you’ll be able to just transfer creatures without a workaround. All the info we have at the moment is that you’ll be able to bring in “select Pokemon from past games to the Paldea region.” I’m sure that will go over well!