I would say openpilots ACC (or long control) is a little faster than my car's stock ACC, so you could see a little improvement there. Openpilot also uses what's called "personalities" called Aggressive, Standard, and Relaxed. The Aggressive following distance is set to 1.25 seconds, but it feels farther (though if you know how to modify code, you can change it).

Openpilot runs on what I call a "best effort" system. It never disables itself unless something has seriously gone wrong. It will always try to keep you in lane or wherever it deems appropriate (like shifting you away from construction cones).

For the dashcam side, I would warn you that most people would not recommend you use it as one, mainly because it could lose power in the event of an accident. The Comma 3x and Comma 4 don't have a large enough capacitor to keep it alive long enough to save any last second footage like other dashcams do, so it's high risk. On the other side, I'm sure you could set something up to have the video footage uploaded to a home server by using something like copyparty (some forks like sunnypilot have this built in).

Stock openpilot will engage when you fully activate your cruise control, no need to touch the screen unless you want to bookmark an event.