You'll have to download it entirely again when it's going to update, so if you have a slow connection you'd better just wait.
As for multiplayer, it has local and LAN/IP direct. So you can play with up to six people on one computer, six people on six computer in the same place, or six people "online" by using a VPN server emulator. I recommend Radmin, it's free and very easy to use. You turn it on, choose any channel, have your friends choose the same channel, and send them the IP given by Radmin. If you join, you copy that IP, go to online, Join, and use Ctrl+V. It's a bit technical but once you get it it's a matter of seconds, and it's as stable as the host's connection (so… uh maybe not yours, lol). Personally, I see it as better than SSF2's approach as my connection is better than their servers, also they have none in my country…