To the OP, I'd say 'well' and 'yes' to your first two questions but everything is relative. Better answers might be possible if you could describe your mission and what types of aircraft you are currently flying. I don't know the answer to your other questions.
I have a 160hp O-0320 RV-4, I live in the mountains, and am always flying in the mountains. Home base elevation is 5,000' MSL and I typically operate from airstrips that are 7,500' MSL and higher at density altitudes up to about 12,000' DA during the summer. Prior to January 1, 2020 (ADS-B) I frequently cruised at 12,500' and occasionally higher. Haven't done that since that date unless getting over ridges. The only reason I go that high is for favorable wind on a long cross country. I'm usually MUCH closer to the ground as I love seeing the details of the terrain.
In my opinion and within limits, mountain operation is more about the pilot than the airplane. A 160hp RV-4 is VERY capable but still has its limits. In the mountains, more power is ALWAYS a good thing. The ability to fly slow and maneuver is also a good thing. You can very comfortably cruise around those tight valley's at 70KIAS. The RV-4 slow speed maneuverability is pretty tough to beat and you get incredible visibility to boot. However; airplanes are a compromise. A friend with a Carbon Cub has more fun in the backcountry (able to land at more of the airstrips (short/rough)) than I can but it's six hours for me to get from New Mexico to Johnson Creek, Idaho. It's two days for him. Compromise. If you plan to haul two large people and a ton of camping gear into the backcountry, the RV-4 is not the best airplane. I do pretty well with one (large) person and 'sufficient' camping gear.
Here are a few videos of my RV-4 operating in the mountains. Not sure if they'll help but might give you some insight. Feel free to poke around on my YouTube channel (https://www.youtube.com/channel/UCrY...8piboPjsIuVkA/
) as there are takeoff/landing videos of a bunch of backcountry airstrips (Thomas Creek, Upper Loon, Negrito, etc.).
Landing/Takeoff at Big Creek: https://youtu.be/hxBSY4tWHlo
Approach and landing at Johnson Creek: https://youtu.be/xu3XmmIFdLI
2019 Backcountry Trip: https://youtu.be/hdQkRgyw4jc
2021 Backcountry Trip: https://youtu.be/Bt6IOlHAQ1g
The thing that these videos do not show is how capable the airplane is climbing up over the 10,000' MSL ridge and then dropping back down into the next valley to land at another airstrip. Excellent performance.
Another of the compromises is the big hershey bar wing. It works great but can be a bit of a bumpy ride when the mountain air is all stirred up and going fast. I have some mountain flying rules of thumb to help avoid that.
A CS prop is far out of my budget but I did install a Sensenich GA. It is VERY easy to change pitch settings (on the ground). When I really need takeoff/climb performance, I change the setting. Certainly not ideal but it works for me - another compromise.
Hope all that helps...