Am I correct in saying that I can keep a copy of the "player.blueprints.4.db" file and paste it after my weekly wipe (not forced wipe) and that will allow my players to keep the blueprints they've already researched on my server?

correct

How to wipe server? You change server seed in the batch file and start server. (Optional: you can free space and delete old map and sav files form your server disk but not needed)

So you do not have to backup anything like player.blueptints.4.db or keep copy etc. They will not be lost or wiped unless you manualy delete them and start the server as BP wiped.