Sorry I can't answer any of the questions directly, except for #4.
One thing to get out of the way for those of us who live in the US: Tribune Media Services dominates the electronic program guide industry in the US. Coincidentally, I've never found a FOSS TV EPG in the US. The bottom line is that you're not going to find an easy way to make a PC into a full-featured DVR for free. If you're a cable subscriber (required to get HBO, and thus HBO Go) you might as well use their DVR unless you have a TiVo with a lifetime subscription (like me) and are willing to fight your cable company tooth and nail to get them to do what they must do by law.
I carry a Hauppauge 950Q TV tuner that works with some hotel cable systems, and can record OTA TV programming if I'm close enough to the transmitter. It only works on one channel at a time, but it's better than nothing. The MPEG-2 program stream file that the included software puts out can be streamed or converted to something like H.264 to save disk space. It's useless with most home cable systems because cable carriers don't give anything away any more.
A few months ago I bought a Roku XD to supplement my TiVo, and to use while on the road. Although the price was right (it was on sale), I found little else to recommend the Roku. It's Wi-Fi-only, which puts you at the mercy of the unlicensed airwaves for streaming video, which is a gamble at best. It has a micro-SD card slot, which you'd think would be ideal for stream buffering. The Roku only uses it for holding games, which I have no interest in. The remote is simple, but lacks all but the most basic functions. For a TiVo user it's not good enough for handling video. But it's tiny enough to chuck in a briefcase and go.
Last month I picked up a Netgear NeoTV MAX for not much more than the Roku, and was surprised to find out that the Netgear product uses the same tiny case that the Roku does. But it comes with a real Ethernet port and a full function remote with a slick QWERTY keyboard on the flipside. And the SD card on the Netgear product is used to buffer video!
I use the DLNA service that's an "included option" for OpenSUSE that uses a simple text file for configuration, is easy to set up and "just works" once it's set up. It works with my TV and the Roku and Netgear boxes. I've tried to get Windows 7 to do DLNA with no joy. There are 3rd party programs for Windows that might actually work.
I really should cancel my monthly Netflix service because I'm not a big movie fan, and the TV shows on Netflix are at least a season old. Hulu Plus OTOH only offers the most recent TV episodes (in HD), which is almost as bad. Amazon charges a couple bucks per episode (you have to buy them), but at least has the missing episodes when you need them. (Amazon is on my TiVo; I don't know of any other home theater appliance that supports it.)
If you're happy with basic cable TV shows, watch them in (or near) real time, and want to lose your cable company then Hulu Plus is what you want. If you are into movies and never, ever watch what's on TV then Netflix is your product. If you're an Amazon Prime customer...you're an Amazon Prime customer and might as well use the free stuff it offers.
That's about all I know on the subject.