Scope and mount questions

Hey guys look at me bugging you all again ha ha.
I have a Savage 11VT i got from Dick's Sporting Goods a couple weeks ago. My question is if I plan on doing mostly 500ish yard shooting for now but I want to go farther in the not too distant future should I go ahead and buy a big 20MOA mount for the scope that I plan on using or will that have adverse effects on my ranging that im shooting now? the scope I plan on buying this weekend is a Nikon Prostaff 5 with 4.5-18 magnification and a a 40mm objective lens, would that be able to take me out to say 1,000yards next summer after I get my hand loads down? This is really my first trip into long range precision shooting. I just finished a monster of an AR15 build but that's my 50-300 yard toy. Sorry to bother you guys with so many questions but other than my little 2006 year model Mark IIF this is really the first "precision" rifle I've owned lol.

I'm a huge fan of the SWFA SS line. You get a lot of scope for your money @ $300 and you will get everything you need out of it to start playing around with some longer ranges. I currently run a 12X42 SWFA SS on a 308 I built last year. To me you don't get much better of a scope till you jump up to the $900-$1300 price tags. I also run a 20MOA base on that rifle because I designed it purposefully for long range shooting. I can also chamber it in anything within the 308 to 30-06 class chamberings, so I left it with room to grow for when I am done playing with the 308.

How is the low light operation of one of those scopes? The only reason I am really looking at the nikon is for the adjustable power and the side focus there as a left hand turred rather than a fron lense adjustment. I'm headed back home to work as a deputy in my home state before long and their "sniper" is using his own stuff from his personal collection and I wouldn't mind taking his job here in a couple years after he retires. I have a short action so I couldnt run a 30-06 but I do plan on this rifle being a long range gun sooner than later.

The light tranmission is good, but they are fixed power. Parallax adjustment is in the rear. Here is what I am currently running http://swfa.com/SWFA-SS-12x42-Tactic...pe-P53714.aspx. better reticle offered as well for ranging and hold overs.

Yeah the Nikon I'm looking at also has the mid dot reticle which I like because I can have a 300 yard zero and use the dots for everything from 50-800 yards. I've never been much of a Kentucky windage kind of guy.