Having no experience w/ the RRA Varminter all I can throw at you is this:
If I were looking for a set-up for Coyotes, my choice would be a 20" Bushmaster V-match. I prefer the chrome lining over non-chrome and the V-match has the Chrome bore. I've had the V-match as well as the 24" Bushmaster Varminter. (The Varminter is not chrome lined) Both were exceptionally accurate. I traded the V-match to my brother after using it to much satisfaction for ~ a couple years on P-dogs and yotes. It's on my list of firearms to replace. The Varminter was too long and cumbersome for my tastes although it looked very nifty. On top of that, the V-match is less expensive than the Varminter as the Varminter also has the BFI 2-stage trigger, which again- I didn't care for either.
As to your accuracy question, shorter barrels can be just as accurate as the long ones IMO, it's just that the long ones lend themselves to be more forgiving... It's always the shooter more-so than the firearm when accuracy is the question. While long/bull barrels help w/ settling the weapon for a steady shot, I don't care for a rifle too heavy to be carried. When hunting, carrying is usually a necessity.
Purchasing the lower and upper seperate, doesn't seem like much of an advantage IMO. If you're wanting to save money, the best way would be to build from scratch. Further, if you purchase complete, it'll have a warranty which is sometimes comforting but I expect weapons in this price range to be perfect from the beginning. (On the Bushmaster Varmint/V-match they'll always get the front sight on w/ no cant.... Since there isn't a front sight on it!
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HTH, and if not, free BTT for you. Welcome to ARFcom rjh34.
Sly