"What is an authenticator, and do I need one if I'm only playing StarCraft II?"
An authenticator is an optional security device that comes either as a dongle, ( which can be purchased for $6.50 off of Blizzard's online store, ) or a free app for your Apple iOS- or Android-powered device. Once you link the authenticator to your account, you'll need to enter a randomly generated set of numbers, along with your password, in order to log in. Due to the rampant hacking of World of Warcraft accounts, they've become commonplace in Azeroth. You might not have the same level of investment in your StarCraft II profile as you do in a WoW character, but security is always a good thing, and it's easy to get your hands on.
"How will custom maps work? Will I have to open any additional ports on my router to get them?"
Not a single port will have to be opened, no. The new Battle.net completely removes that obstacle by having all the maps hosted on Blizzard's servers! If you want to play a game, choose it, download it, and let Battle.net do the rest.
“I heard that Blizzard is going to charge me to download custom maps. That seems really uncool.”
Not exactly true. At launch, there will be no content store in Battle.net, so all custom maps will be free to download. According to Lead Producer Chris Sigaty, roughly a year down the road they'll add a store where custom map makers can charge for their content if they want, much like Apple's App store. The idea here is not to make Blizzard a bunch of money from map sales (though they'll probably take a piece of that pie, like Apple does) but rather to promote StarCraft II as a platform for developers. If a mod team sees that they can make money modding StarCraft II or mod StarCraft 1 out of the goodness of their hearts, Blizzard's hope is they'll jump to StarCraft II and make high-quality mods that are worth paying for. In the long run, it could be a great thing for StarCraft II players.
“I have a question you haven't covered!”
Good thing we've got a comments section on this very thread! Leave us a question, and we (or our very helpful PCGamer.com readers) will do our best to answer it for you.