You can keep the cutting edge at 30 degrees if you want and back bevel at 20-25 if you find that makes the sharpening easier. The narrow 30 degree angle sould cut nicely.

If you find that the edge is not as durable as you would like, just sharpen at 40 degrees on the sharpmaker. Either geometry should work well. 40 will be less work to maintain because the 30 degree back bevel is already well established.

I would keep the 30 degree edge as long as it seems to be working well for you. The S30V steel is very strong and should be able to hold up with a narrow 30 degree angle. And the narrow angle will cut more aggressively.

But really I doubt the difference would be that noticeable either way. The most important thing is whether or not the knife is sharp. That will determine how well it cuts far more than the exact angle.

As for closing the knife one-handed, I think the most controlled way to do it is to keep all your fingers on the handle and gently touch the spine of the blade (this is the dull side!) against your thigh after you release the lock. Then pivot the handle slowly down onto the blade. All the usual disclaimers apply about keeping your fingers, etc. out of the way of the closing blade whenever it is unlocked.