1) Those will work, and so will the factory Savage rings for your current scope. Personally I'd prefer Burris Signature rings.
2) Nothing wrong with upgrading the factory plastic stock.
3) I'm not a fan of Nikon, in my experience their warranty is worthless. Buy quality optics, keep your Centerpoint, and you can remount it move the good scope to another rifle if you want to in the future, with no money lost on a resale.
4) Start by clipping 1 coil off the spring, that drops the trigger to around 4 lbs. I can't recommend clipping more than 1 1/2 coils.If you don't like it you can still get a Rifle Basix trigger.
5) Don't bother.
6) You're going to run into a lot of Savage envy out there. Some people can't deal with the fact that your "cheap Savage" shoots better than the safe queen they spent several times as much on. Head over to savageshooters.com for useful advice on the rifle.
Here's the Axis I put together recently:
It's got a Vortex PST, ARP barrel in 6.8spc, JAL linear comp, trigger job, and a swirl dipped camo paint job on the factory stock. It will get a Boyds stock this winter.