Pretty much required, not recommended. No reservations for breakfast or lunch.
It varies from ship to ship, the concierge will give you instructions once onboard, but basically yes, the concierge will escort you off the ship. On Wonder in June it worked as you described and there were a few time choices.
You should receive an e-mail from them 5-8 days before your cruise. I wouldn't rely on them for excursions; hopefully you have those booked much farther in advance. We only really used them pre-cruise for CK reservations, to make sure the CK staff was made aware of my niece's severe food allergies, and to have our balcony separators unlocked since we were traveling as an extended family with 3 side by side GS's. Feel free to ask them anything you can think of.
Yes, the concierges are usually there for a few hours in the morning and then late afternoon/evening. The SL is open 24/7. There is a self-serve espresso machine for making coffee, lattes, cappuccinos, etc. Continental breakfast is served every morning. There are usually snacks in the afternoon. There is a 3-hour nightly happy hour with an open bar as well as snacks (5-8pm or so). You also get free beer, wine, Truly, hard cider, soda, bottled water from SL bar from 11-11 daily.
Of course!
That covers a lot of it. If a show or experience is sold out, the suite concierges may or may not be able to get you spots.
Enjoy Sky Class! We're not normally suite people but we had an amazing time taking advantage of the perks when we were in Sky Class.