As a Linux sysadmin of 17+ years (and now a CIO), this is the best advice posted to this thread. After you complete this I'd suggest Linux From Scratch (http://www.linuxfromscratch.org/) as it'll teach you about the inner workings of a Linux system, which is vital if you want to be a really good sysadmin (a good troubleshooter understands the internals). I would hire someone for an entry level position if they went through this process and if they could explain things at a deep level as that would show me that they have the potential to take it to the next level.
Major syncing issues that will lead to a ton of support requests. The number of users using the application didn't seem to make a difference - our user count slowly increased, then decreased at the end. Various people had sync issues the whole time.
I'd like to see something like this redone in a lower level language - it seems like PHP isn't well suited for this task.
I have been using the same (ish) Air that you're looking at for about a year now (this is my first Mac). I'm getting rid of it and grabbing a Dell XPS 13 Developer Edition - the screen resolution on the Air just isn't good enough, and the OS is a joke compared to Linux.