So can I attach a Sennheiser MKE-300 or Sony HVL20-DW2 to the HC7's hotshoe? I know it has a plug-in mic connector, enquiring about the implications of hotshoe and the physical connection - it looks recessed into the top even when cover opened (haven't seen cam in person)

It's not a standard shoe, but you can use an adapter...

http://shop.dm-accessories.com/products/ais-flat-universal-shoe-mount-for-sony-camcorders-with-ais-mount

this also works, with lighting or wireless on the xtra mount.
wz

http://www.markertek.com/SearchProduct.asp?item=VB%2D50&off=0&sort=prod