Hi,
I can hopefully answer your first question but not your second as I do not have parking sensors myself.
The feature you are referring to is what Lexus call smart entry as opposed to remote keyless entry (where you have to press a button on the key fob).
When i test drove an SE-L with Nav last August it did have smart entry and i was told by the sales person that it was part of the Nav package, however I believe that is not the case with the current SE-L model. It seems that only the Premier has smart entry. My F-Sport does not have it either.
One way you can tell for sure will be to look at your door handle and see if there is a small oval shaped indentation (about the size of a Tic-Tac) on the top surface of the handle above the keyhole. If there is you have smart entry, if not you don't.
I actually wanted smart entry myself at first, but now I'm quite happy without it, I can just jump out of the car, put my hand in my pocket and lock it as I walk away as opposed to stopping to touch a small sensor on the handle.
Keep enjoying the car!
Matt