Looking really nice Johnathon. Yes, going to some i35 or even i40 rims would help the tyres not squirm as much at lower pressures, however, with such big tyres, you sort of have to adjust the pressures depending on what sort of terrain/trails you're going to be riding, or at least that's what I found. If I'm riding slower, techy trails, then running 3" F&R I can run about 10-10.5 front and 13-14 rear, but if I'm on faster flowier trails with more high speed turns, then I have to bump up a PSI to help stop the squirm.
As to tyre width, I'd say don't go narrower than 2.6", that's the smallest I've found I can run and get the benefits of the "PLUS" tyres to help "replace" suspension. If you're going to go for the narrower tyres, then your existing wheels/rims should work just fine.