Craig,
I'm not sure about DVB-T2 hardware, I personally use a TBS (DVB-S2) card which I'm quite happy with and I know some people are using a TBS T2 equivalent without issues.
You'll definitely be fine with that hardware for serving content, almost ANY modern PC will be capable of that :)
TVH does NOT currently (and no intention at this time) support interactive content. However most of the interactive streams are simply just standard services that aren't NORMALLY in the channel list (but nothing stopping you including them), of course you still won't get the interactive menus etc...
With regard to the olympic streams, I don't know how this works on DVB-T, but although they are accessible via red button they're also standard channels in their own right (i.e. they're in the standard channel list).
Adam