There are no "one size fits all", if that's what you want then best stick with the defaults and get used to them.
Otherwise it'll depend on your own feelings and what you're trying to do, so experiment.
What are the recommended settings for these?
I see Max Horizontal Speed, default to 15.0 m/s, which seems to be set at the max value.
Max Ascent and Descent Speeds are both set at 6.0 m/s, also the max values for those parameters.
Brake...
The 48hrs will start from the time the drone has been turned on irrespective of whether it's been registered to your account or not. With the Air3S, it would not allow you to fly unless you activate the RC at least, the drone and RC are bound to...
You got a code? If you got a code, there is no clock. You can enter it here: https://service.dji.com/care/active
I'm not sure if you can fly that drone without activating it; probably not.