Well, the additional RAM will be a big performance boost, so that's a good idea.
My first thought when you described what you do right now is that it's too complicated, and too prone to environmental failure (flood, fire, theft.) Your new plan makes much more sense -- keeping the second (now third) drive off-site, and backing it up every few days is a very good idea.
In my experience, it is MUCH easier to back up whole drives onto other whole drives, rather than having different partitions and drives for different kinds of files. Again, good idea.
I have a Mac tower at my studio, along with a server which houses my entire RAW file collection. I back up the server onto external hard drives, which I keep at home. (That server is also backed up to our tape silo downtown, but that's an advantage of a staff job that is usually unavailable to independent photographers.) There have been several occasions when I was glad to have the off-site backup available.