Sleepless ~ I have done quite a few b2bs. Answers to your questions:
You will receive a letter the last day of first cruise telling you where to meet the last morning of first cruise to be escorted off the ship by a ship's officer, through customs and then back on the ship again. Yes, you do have to wait until everyone from the first cruise is off the ship before being escorted through customs.
When escorted back on you will receive a new S&S card and a new S&S account will be set up.
The room stewards like you to leave so they can clean and if you tell them you will be staying on for a second round they will get your room done so if you want to you can return after you have gone through customs and checked in for your second cruise. Every time we have done a b2b there is always a fruit basket/champagne waiting in our cabin at the beginning of the second cruise.
If you want a Welcome Aboard photo taken at the beginning of round two tell the ship officer escorting you and they will make it happen.
If you want any adult beverages from the duty free shop for your second cruise wait and buy the last day of fist cruise that way you can take your bottle(s) with you to your cabin. It used to be those purchases would be delivered the last night of first cruise but recently they have started holding until end of second cruise.
If you like your table and wait staff during the first cruise and want the same table/staff for round two tell the maitre d during cruise one.
Choose sarcasm. Always.
I'm allergic to stupidity. It makes me break out in sarcasm.