Couple of bits of advice to anyone doing this:
Firstly get your own IPs from your local RIR. Have your co-lo provider publish your routes, but they will be YOUR IPs. if you co-lo provider sucks, you can move and keep your IP space. (This is vital for email, but I recommend it for everyone).
Secondly buy a Out of Band Management card with your server (iDrac for Dell, iLO for HP, etc) these cost fairly little and will save you hours of access / remote hands. They will pay for themselves, you can even boot an ISO from your laptop over the internet. Get your co-lo provider to give you an extra uplink for this and give it a separate IP (use one of the providers range)
Thirdly consider Mission Critical support on the servers from a solid vendor (In australia I consider the enterprise vendors Dell, HP, IBM and Acer, and of those I will only use Dell or HP). 4 hour response means you don't need as much spare hardware, and you can have things fixed FAST. I have only lost 2 disks in a rack of servers over 4 years. Both had a replacement in place within 4 hours (once at 1am).
Fourthly look at a good Virtualization solution. We initially went oVirt (Open source version of Red Hat Enterprise Virtualization) but ended up migrating to VMWare. VMWare Essentials Plus costs us $15K for 3 years in extortionate australia prices and is worth every cent. It provides Backup (VMWare Data Protector), Failover, Virtual SAN, Live Migration and a heap of useful features that save huge amounts of time.
Finally if your going to grow consider getting a rack (or half / third of a rack). This will likely give you unescorted access to the data centre, and is often not that much more then a few RU of servers (depending on the DC and racking availability).