Is it possible to use 5 blades as an SQL server and the other 5 for the website application?
you should do it.
While it is "trivial" to do it for Sql Server, for a website it is not so trivial. If you have different domain and/or subdomain then may be you can runs in in a separated server but, usually 1 server is enough for a website application (since most of the work is done by the database). Also, it is possible to use a separated server for cache, for example memcached.
Blades are nothing more than CPU and Ram alone. You will need additional storage for use with that unless you are comfortable with low HDD. Another thing you would need to look out before you buy blades are the power consumption, they hook up on 208v circuit x 2 or for redundant its x 4.
IPStrada When uptime counts.
Warren Buffet: Honesty is very expensive gift do not expect it from cheap people.
I wouldn't recommend using the older blade generation for webhosting of any kind, they suck up way to much energy, even with the higher efficiency PSU's.
But, to answer your question: just external storage. iSCSI if you want it cheap, Fiber Channel if you want the high-end stuff.