Is it permitted to give a USPS Postal carrier a priority mail or media mail package that already has enough postage stamps on it to have paid for postage and then be able to obtain a tracking number receipt from the postal carrier or must all priority and media mail packages be handed to a clerk at a post office?
Is it also permitted to glue down an entire pane of 50 never hinged stamps to a medium-large box, or do I have to separate each stamp?
You definitely do not need to separate the individual stamps. Just yesterday I got an envelope in the mail where the sender used a plate block of 8-cent Gershwin stamps (a big slab of 12 stamps with selvage) for postage.
I always take parcels to the post office for mailing, so someone else will have to answer your first question.
I believe that if you wish a tracking # on your package you must go to the local USPS Station/Branch/MPO to obtain, as the local carrier does not have the ability to apply. (Also, the clerk will ask if you want signature verification or just delivery verification.. upcharge on the signature verification.. salesmanship)
I use stamps on all my outgoing packages. Anything < 13 ounces can be left in outgoing mail or dropped at the post office without having to hand to a clerk.
On my first class parcel packages I use a USPS Label 400 which is available on the usps website. This is the tracking bar-code and is included in the price of the first class parcel.
For larger packages, I tend to put all but $1.00 of stamps on the package. The automated machine has a minimum purchase of $1 and that purchase allows you to deposit in the drop or leave on the counter without dealing with a clerk.
I also use the Label 400 for tracking and I mail right from the mail box. Recently I mailed a Priority Mail Medium Flat Rate Box right from the mail box with $13.65 of postage on it. I used many higher value stamps, but the entire top of the box was still covered in postage. I left a note with the package explaining that I affixed $13.65 postage as required. Not a problem in my area, we have understanding mail carriers.