I am considering the purchase of a Rock River upper. It looks like it really is a perfect bolt on....but....

Should I be looking at a different buffer spring? Anything on the trigger group need tweaking?

What kind of lower do you have??  My M&P15 lower has a crappy trigger that will be nice to upgrade but not absolutely required.  Other than that my RRA Carbine length upper dropped nicely onto the M&P.  The Upper comes with 2 buffer springs but I am using the stock spring.  You will need sights or optics, other than that if you can get it, go for it.

I have an Armalite lower with the 2 stage adjustable trigger, collapsible stock. The rest is all standard Armalite parts kit.

To use the .458 SOCOM upper you need nothing new on the lower.  It is designed to run with standard rifle and CAR buffers and springs as well as standard 5.56 mags.  No trigger tweaking or other such nonsense.  People do tweak things on their rifles but it is not needed outside of personal preferences.  If you are running a HB or XP spring on your current AR lower you may find the .458 upper will not run and you may have to put back in the standard items.  With XP springs and HBs the uppers will usually run OK with some loads but not all of them.  With standard springs and buffers it will run with any ammo you feed it.
The SOCOM has been known to auto collapse standard M4/CAR type adjustable stocks, damaging them badly in the process.  You may want to run a fixed A2 stock or a stronger telescoping stocks such as the UBR, CTR or ACS.  If you run the ACE M4 SOCOM stock it MUST be fixed into position.