You should already have DT DB spokes in them wheels, but probably not Revolutions
A costly, pointless exercise changing at this stage, but later when you're chasing the last bit or building up wheels anyway, why not
You'll be wanting 130g/150g inner tubes and 450g to 550g tyres before that.
Spokes x32 , DT Comp (2/1.8 butting) 262/264mm = 192g Which will probably be similar to what you have.
Revs are 148g for the same length (2/1.5 butting)
Brass to Alu nipples are iirc 30g lighter
(bit less than 1/3lb saving for a pair of wheels)
(P.S. XT and 517 will be heavier wheels iirc given the same spokes and nipples.)
The Fox will be the better fork, they are 5 years newer.
You said these forks where 4lb?
Light forks will be around 3lb, so only a 1lb saving.
Rigid forks are 1.5 to 2lb in weight alone, but you're not going there
You've still not replied with the length of this current stem ?
I really doubt the general weight loss will do much to the ride, other then some lighter modern tyres (or even Amber wall MythosXC's) and a tweak in the steering responsiveness and your balance on the bike.
They are a different style of ride between both your bikes.
Get the basics, sorted, ride, ride some more and then worry about it again and drip feed new lighter bits on and move the old to that extra frame you now need to buy