Yes, as far as I understand it is important we all roll characters on the same server. I will aim to be online for when the servers go up on launch and also sit in the web site chat. Will then strive to announce our server choice in an as spammy way as possible. To prepare, it's important you check our Internal threads on the topic, like the "RP or not RP server?" vote.
I will also strive to make this clear via Facebook / Twitter etc - I am the queen of Spam, baked beans and spam.
If you find yourself forced to mercilessly slaughter your teammates because they become infected with some rare mutation, keep in mind that you are only doing your job -
They would do the same for you.
I won't fill 3 or 4 slots so quickly after launch, so I'm sure I'll have at least one slot free to roll a character on the server we'll choose, once we choose it
The main issue in your scenario is simply that nicknames are unique in the game and I don't think renaming is supported. So you might want to refrain from rolling your "main" nick until you know.
I wouldn't count on reservations surviving that process though. At least for very popular nicks (you know, stuff like real names or similar) deleting it to recreate half a minute later might already be a race condition with someone else that also wants to roll a "Jeff" or "Ohforf".