First, don’t go with free hosting services, ick ick ick. 
From my experience, it’s a lot better to go with separate sites. For example, I had the one big site that covered casinos, bingo, poker and sportsbooks. It was a great site, but it was becoming a site that people would add to their favourites, not one that people would go to, then from there go to a gambling site. There was just “too much” for them on there, and so my conversions weren’t too great. I’ve now split everything up, and not only is it a lot easier to manage, but conversions are a lot better. There’s a thing called “too much”, and my old site had that
Of course, it depends how you run the website. I mean, look at Dominiques, that covers everything under one domain however is done exceptionally well, as content is kept apart and is more of a directory.
Now, if you’re wanting to build a community, and offering poker advice and strategy that can be a good idea(mentors, proteges etc), then one main site is probably the best way to go, and submitting articles to other sites with linkbacks won’t hurt.