New realms, and everyone starts level one
Forever opens fresh, which is the whole appeal and the whole problem: the people who get to the cap first are the ones with the week off. A starter pack is how you keep up without taking one. Levels, a mount and professions bought together cost less than the same services one at a time.
What can actually be delivered before launch
Not much, and the page says so rather than taking the order quietly. Before the realms open, what you are buying is a reservation: a slot with a booster who starts the moment they can log in. Gold, dungeon tours and the hourly all need live realms and begin at launch. If you order early we hold your place and tell you the day work starts.
You choose whether anyone signs in
Self-play means you are in the group and nobody signs in as you. Account share means a booster plays it while you do something else, which is cheaper and faster and is the option that involves a password. Account sharing is against Blizzard’s terms, which is true of every seller in this market, so self-play is offered on everything here rather than as a token alternative.