I'm a little confused...do you want some drives active and others not?
How much data needs to be active at once?
Are the other drives you are connecting just going to be backup drives?
Sorry to hear about data loss...there was an interesting article about HDDs and failure the other day....it's pretty much a guarantee at some point (especially after 5 years or so)...interesting data.
If you are looking to use drives as a backup, you could just connect via eSATA or USB and backup data.
If you want them all in the system or eSATA and want hot-swap, you need to make sure you have AHCI (motherboard, and configured correctly in the OS).
If you are looking to better protect against a drive failure, a RAID volume with a hot spare might be in order.
I have a setup where I have a dedicated tray for a backup disk...something like this:
http://www.amazon.com/Kingwin-Aluminum-Mobile-Triple-KF-813-BK/dp/B000CDR8OG
That way I can backup data to that disk, take it off site (my office), and put in a new disk for the next backup.
There is an option to connect RAID towers to your current computer that use eSATA as a port multiplier, I believe...
With more info, I think we could point you in the right direction.