Code (IRC) minimum for a 'habitable' room is 70 square feet, so you are legal, assuming your local jurisdiction doesn't have stricter rules. You would have to have a big enough window to meet egress codes, and most areas don't consider a bedroom unless it has a closet. As for realtors- my mother's old house had a 6 X 7 BR, with a closet, and it was included as a BR.

It very much depends on your style of living; how much of the area is actually walkway to get from side to the other or across/behind the space, how many people will be the usual number sitting, do you want extra space for parties or groups, is your furniture sleekly minimalist or wide-armed/bulky, and is the area for conversation only or will there be a TV at one side, will the kids be having friends or playing in the area ... i.e. you need to know what is going to be done with the space before you can guess at the amount of space needed. Also consider that many GRs are edged by a kitchen island with sit-down space and the sitters are actually intruding on the GR area, and extra walkway in the GR space must be allowed to get past the sitters. I've seen well-planned GRs at 16'x18' and uncomfortable/poorly planned rooms that were more than 24' to a side. In fact one of the worst I've seen was about 24x 28 (they entertained several times a year and had to allow for the occasional extra bodies), which was acutely reminiscent of an airport waiting room. A superb decorator might have helped, but to me it was simply a large awkward space that was comfortable mostly when there were an extra dozen guests. And one of the best was of nearly the same dimensions, with great care taken in furniture arrangements and walkways. BUT, in each case, the owner liked it and that's what counts.

No, you don't want to crowd the furniture into the pool table's area. Anyone sitting would not enjoy being either stepped on or poked with a cue. As one who followed the 13x17 recommendation, I can tell you that in real life, it would have been lots more comfortable with another couple feet (open space) in both directions. Also, people playing will stand around or at most, sit on bar stools high enough to permit a good view of the table -- low furniture is pleasant for many things, but not for watching eight ball. If I had it to do over, I would use not less than 20x20 and dedicate the more spacious side to a narrow counter with nicely padded tall bar stools. Add more feet onto one end for the pub table/chairs and don't forget walking space around them. Depending on the size/style of table and chairs, a 20x30 room won't seem spacious. My personal opinion, but TVs don't belong in the same room as hard balls -- cohabiting has a high potential for damaged screens.

We are in mid-construction on a screen porch that is just a bit over 8' x 11', so very similar in size. I would have gone larger if I could, but we have already maximized our lot coverage! The porch is replacing an existing (well, not existing any more!) deck that we never used because it was either too sunny/hot or too buggy. We will have two loveseats situated in an L shape in one corner, two small square tables to use as coffee tables (or ottomans), and a couple of folding chairs to stick in the corner and put into service as needed. Anyway, all of this is to say that your size isn't too small -- depending on what you want to do with it!