iMac 27inch + SSD and HD + Filevault + Yosemite

I have an iMac 2011, 27 inch model.

It's got a 1TB hard drive, but I want to add a SSD drive then upgrade to Yosemite. I also require FileVault 2.

How hard is it to add the SSD drive, then do a new Yosemite install?

Is it difficult to have the system/applications on the SSD, and the userdata on the HDD?

What are the best practice suggestions I should take?

Will FileVault 2 cause any problems? Will it encrypt both the system and the user data?

THanks