I put a 1TB hdd in the night I brought it home. I beleve it was just the 5400, no clue about the 7200, but the one I have seems to work just fine. Also it literally took me 5 min to swap them out, super simple.
I've played quite a few games on it. I beat Killzone Shadow Fall, Lego Marval, Resogun & Contrast all pretty fun games. I've also played a ton of Dont Starve, that game is super addicting. I've also put about 15 hours into AC4, and still have a lot more to do in that game. There are a few others, DC Universe Online, Flower, Sound Shapes, Warframe, Doki Doki Universe & Blacklight that I've downloaded but haven't really had a chance to play. Finally, I started playing Outlast last night, and man oh man is that one freaky game. I am really enjoying it so far, and plan to play more. PS+ really makes any of the Sony systems worth owning. The four free games they've given away on the PS4 have all been really good.
I've also messed with the remote play quite a bit. It's a really cool feature, but I think it works better for some titles over others. Like Resogun was a little to fast paced, and the minimal lag I experienced was a bit frustrating, but AC4 is fantastic, and the majority of the 15 hours I've spent with that game, has been played over remote play.