If you wish to access any of the digital channels (which includes HD) then you'll need a STB since those channels are encrypted and you need a STB to access them. The only way to record HD is via firewire, but it has been problematical. See the following post on Recording HD and see the link to the Rogers firewire thread in there.
There has been some recent discussion on recording via the "analogue hole", that link is also in the above. Other people will have to answer your other questions, but those may also be addressed in the above links.
Please put your location and service provider into your UserCP Profile (location). This helps us help you. Here's a thread useful for newbies to the forum: