yes you can use an SSD for os and Dont worry about the ahci thing it should do the setting for automatically (the mobo)
Not sure why you'd bother with win8 unless your tv is touch screen. But thats my opinion.
Not sure what you mean by GPPAs?
That graphics card is old, although you dont seem to need much more performance id still spend the extra £10 and get a gt 610
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does c/w 500w mean "comes with"
if it does, dont buy it, it'll become a door stop and probably take other components with it.
The psu is a very important piece of the pc so dont skimp on it.................