Welcome to the world of Frontier owners!

. I'ts like air conditioning in a car - once you start, you'll never go back...Mine is in .300 WSM but I'll try to answer your questions.
In the bush I use either a 2.5 X Leupold scout scope or a red dot on the forward point. I find I'm using the red dot more often.
I also have the rear set up to accept a quick detach 3X 9 scope. I ise it for load development or if i'm hunting open areas.
Mine is extremely accurate- 3 shot benchrested groups with handloads run about 1/2 inch at 100 yards if I do my part. I put a Timney trigger on it so my pull weight is about 2 1/2 pounds .Other users have also said they're extremely accurate.
In my mind, the Ruger Mark II is the most reliable hunting rifle out there. ( not to knock Winchesters and Remingtons= they're also quite reliable.
For the bush, I love it

- it defines speed and ease of carrying. the only thing I can think of that would be easier to carry would be a holstered handgun -not that I would, of course.
If it's like mine, you can expect to lose about 25 FPS per inch of barrel relative to a conventional length barrel - so 150 FPS less than a 22 inch barreled rifle. I can't tell you what the point blank range is without knowing the bulllet weight and muzzle velocity- but if you look it up in any reloading manual that has ballistic tables, you should be able to determine it, or perhaps someone on this board more familiar with .308 ballistics could answer you.
again, enjoy!