The reason why 30 fps on consoles seems like a relatively smooth experience is because most console games (especially modern ones) make generous use of motion blur which tends to smooth out the gameplay as well as the fact that most console games are built from the ground up to run at a constant 30 fps, including the way the game is actually outputting the frames (e.g. frame times on console games are typically more consistent for 30 FPS compared to PC due to more optimized vsync and framerate limiting). I've played PC games at 30 FPS and they generally do not "appear" as smooth as many console games at 30 FPS unless you use specific VSYNC or frame rate limiting methods. Also input lag and using a controller vs mouse and keyboard can also change your "perception" of how smooth 30 FPS looks. This is why anything below 60 fps (or 40 fps on gsync/freesync monitors) for me is annoying in most of the PC games I play whereas I'm OK for the most part with 30 FPS in most console games.
Upgrading from a 980 to a 1070 seems a tad silly to me. If you're willing to splurge on a new GPU every couple of years and money is pretty much no object, then go straight for the 1080. If you are on any sort of budget, then I'd probably recommend waiting one more year. From what I understand the 1080 is the first viable card for 4K resolutions, but still doesn't run most games well. Maybe the eventual 1100-line will achieve that, who knows.
My plan is to get a 1060 to replace my five year old 560ti (still runs most games OK), and then get a spanking new card when I update my displays to 4K in maybe a year or two.
But the price difference between the 1070 and the 1080 is quite severe to the point that you can almost get 1070 SLI (currently ~$800-$900) for the price of a 1080 (currently ~$650-$750). Also even at 1080p there are many games that the GTX 980 will most definitely not be able to run at a solid 60 fps with maxed out settings (Witcher 3, Rise of the Tomb Raider, The Division, etc). The GTX 1070 is a solid 40-50% faster than the GTX 980 and if you can find one for <$400 I would say it's a worth while upgrade (even better if you can sell that 980 for ~$200) even if you are running a 1080p screen.
I got my GTX 1080 almost a month ago and I've been pretty happy with it. I use it on my bedroom PC with a 1080p TV and I have to say that while you could definitely consider it "overkill" if you are purely running at 1080p, for me I can't stand aliasing which is why I love DSR (dynamic super resolution) and trust me once you start using DSR, the GTX 1080 stops being overkill especially if you max out all settings in modern games. Not all games are as well optimized as Doom (which can run close to 60 fps on a GTX 1080 even at 3840x2160) and even decently optimized games like Witcher 3 can can chug a little bit when running DSR at above 1.5x on a 1080p screen (>1440p). But DSR to me is far superior than running any form of AA and games not running in DSR on a 1080p screen just don't look nearly as smooth to me. At this point I almost never run any game at the native 1080p res of my monitor, except for Hitman 2016 which suffers significant framerate drops if I run anything above 1080p.
I think it's difficult to properly assess the difficulty of a Dark Souls game unless you come into each one fresh since having a lot of experience in previous souls games will just inherently make the next one easier. Even though there are clear differences between all three DkS games, the fundamental combat mechanics are very similar. For me Dark Souls III was an easier game for me simply because I've had so much experience with all the previous Souls games. I dunno if I could properly say that it's easier than DkS1 or DkS2 since there were very easy ways to become completely overpowered early on in those games. The bottom line is I don't think I'm able to fully assess the difficulty of these games for a new player since I'm not a new player to the Souls series so these games are just naturally going to be easier the more of them I play. Your first Souls games is always the hardest one regardless of which one you decide to play first. Any other Souls games after that are just inherently going to be easier.
Honestly the souls games have always been more about stamina management than health management. Except for certain bosses where dodging their attacks are just extremely annoying due to poorly designed attack animations and/or bad hitboxes, for the most part if you can manage your stamina well then you can survive any enemy encounter without taking any (or minimal) damage. Especially once you learn the enemy attack patterns. As for comparisons to Bloodborne's 20 vials, it's a different paced game. Even though Dark Souls III is a little faster paced than previous Dark Souls games (in terms of speed of combat of some of its weapons), it's still a much slower game than Bloodborne, even when it comes to healing (smashing those blood vials is much faster than chugging an estus flask). Also you can use shields with 100% physical DR from the start. Plus you can get all the estus upgrades in a single playthrough.
I only felt low on estus only a few times in my first two playthroughs of the game and only because I over-extended myself by exploring too much of an area without resting at a bonfire, plus trying to fight too many enemies. I've never really had to use all my flasks on a boss except for a certain late game optional boss that has two separate phases (who shall go nameless.) but I've also played every single souls game multiple times. I guess if you're a newcomer to the series then the 4 starting flasks are gonna seem limiting, but then again DkS1 only gave you 5 flasks from the start so it's not like there's no precedent for this either. Ultimately I think it's a tough balance on either end of the spectrum since either giving you too many or too few flasks from the start is going to cause some grumbling.
The boss you just beat is actually an optional boss. The next area you need to go is past the bridge with the big guys that throw the bowls at you and up a flight of stairs. Through the big door there is an elevator that goes up and down. You need to make it go up and then wait for the second elevator to come up and take that one down. This will take you to the next area.