New installation : advice to save times

Hi all,
I'm new to Zimbra and would like to use it to a new, fresh network.
I'll have around 10 users.
As there current mail server is crash, I'll have to make it ready asap ...

I'm used to Ubuntu server and Debian.

My first question is what OS should I use ?
I saw in the quick Start, I can use Ubuntu 12.04 LTS (64bit) or Debian 5. Is it still up to date ? Can I use Debian 7 ?

Is there common error I should take care about ?

Do you have any advice to give (or loan) me ?

Thanks
Cyril
edit : ( I'm currently reading the documentation )