Unless you have a very good reason - density, etc - I would advise against going with blades.
A good 2U server from HP or Dell would provide all you need in the way of RAM. I personally prefer HP DL380's - I have several with 72+ GB of RAM. You really need to get a better grip on the fundamentals before you start worrying about what kind of hardware to purchase. You need to have reliable power, cooling, security (locked rack / server room), network access, ram and disk specifications, etc before you start looking at the kind of servers to buy.
EDIT - there is no such thing as an all in one guide to servers. I'll provide you with some preliminary stuff to get started. There is a little bit of extra information in here just in case anyone comes across this at a later point in time.
This Tech Republic article does well describing the physical requirements you should be thinking about.
Your existing bandwidth requirements should be pretty easy to determine. From the tone of your question you have a hosted solution somewhere else, either a VPS or some kind of hosting provider. You should be able to locate your existing utilization data. Expect to provide the same amount of bandwidth or higher for your in house server. The same can be said regarding the amount of disk space you require.
You definitely need to have a UPS in place for your server. Without power conditioning in place you are asking for disaster. What happens if the power flickers for one second Friday night? Your website will be out of commission until someone notices Monday morning.
Regarding your disks, you need to have RAID in your server. I suggest either RAID 5, RAID 10 or RAID 6, See here and here. Most any modern server provides this capacity. Consult the server manual for how to configure the RAID as it varies widely by manufacturer.
There are a couple more advanced points associated with running your own server that should be considered as well.
Along with running any server the burden of maintaining backups becomes yours as well. It sounds like this is something that you haven't considered. In this situation you might go with a tape drive attached directly to your server.. In any case it is something you should be thinking about.
Any internet facing server creates some risk for the network it sits on. Use a firewall to protect it from most internet traffic. To minimize risk to The use of a DMZ is highly recommended.