The "standard" rule of thumb most people use is usually 1x per 100m for a combat rifle. That's a good starting point.

If you have the offset red dot, do you REALLY need to get down all the way to 3x? Increasing the ratio between the top and bottom number is where a lot of that extra weight and cost is coming from. There may be some magnification/weight tradeoffs available to you that you haven't considered if you go from a 5x to a 4x or 3x magnification ratio.

The human eye is typically good to about one MOA if you have 20-20 vision. This is a decent approximation of what the rifle is capable of as well. You might get a quarter to half that with a good AR, and less with bench rest, but 1 MOA is kind of the standard for a "good" rifle

Technically, even with a 1x scope you should be able to hit anything big enough to see... but just barely see. The main benefit of a scope is to place your target and reticle in the same focal plane.

The real benefit of the higher magnification is more in target identification than actual effective accuracy. Also, higher magnification can make a paper target easier to see and just plain more pleasant to shoot, so preference plays a role.

Personally, for a practical rifle, where my goal is to "hit" rather than "miss" as fast as possible from field positions, I'd want a 1-4 or 1-6 scope on there, skip the red dot, throw some offset BUIS on. From the choices you listed, I'd go 2-10.

For a bench gun that I wanted to really wring maximum accuracy from, though, I'd get the 3-15x, or even more.