Shuttle barebone SZ77R5, Sapphire HD 6870, i5 2500K

Hi, I'm planning on building my first computer out of bought parts.
I thought that shuttle barebone SZ77R5 would be a good, mobile case.
Me and my father found a good combination with a Sapphire HD 6870 card, a i5 2500k processor and 8gb ddr memory.
These parts were picked after my gaming behaviour. I dont plan playing too high graphic requiring games, but still enough to play most of the common games smoothly.
I'm wondering how good these parts sync with eachother aswell as with the case.
Is there something that doesnt work out very good, please suggest another equalent part if possible!

Also, I'm wondering if my old hard disc (that were used on an old shuttle barebone) would fit into the new system.
I've heard my father talk about that it runs on something called SATA 1.5 while new system would run on SATA 6.0.
I'd require some kind of downgrading in order to make it work? (Right me if I'm wrong).

Please excuse me if I'm using any of these terms wrong or havent explained well enough.
I'm not very good with computers.

Thanks in advance.