On the last night of our first leg we got a phone call from Dining Services asking if we had any requests for the second leg--specifically did we want the same team, have a rotation preference, want Palo ressies, etc. We said that we'd like to keep the same head server but would LOVE a more efficient serving team--got it!
You can check with GS on the last night of the first leg about upgrades, but there's no need to...and if they sell it to you then, you pay regular price (people have reported getting calls about upgrades, especially for suites!) You will be the first people in the terminal to start the second leg, so if there are upgrades, you can nail them then. Yes, if you do upgrade the second leg, you'll have to pack up and vacate the first cabin IMMEDIATELY after you reboard, so any packing up you've done in advance will help. Yes, you'll have access to the laundry rooms regardless of whether you change rooms or not.
If you are keeping the same room, you will have access to your room during the transition time. You'll get a regular cleaning during the time that you are at breakfast/checking in.