One of the most comprehensive bar stool companies is Atlantic. They have a wide range with modern, contemporary and vintage styled ones. If you go with orange then the print you have bought could go in with the scheme. For wallpapers have a look at Romo or Harlequin they have some lovely designs. I do think the dining area could take a feature wall so do look at that, it will define that area. Once you have decided on a wallpaper the rest will follow.

I like both, depending on their use. For sociability, the swivel are great. For writing or some other, more 'stationary' function, the stationary are it. The swivel is too much work to keep it stationary!

If you want the seats to swing out from the island be sure to check that the island is substantial enough to take the load, also that the island is well anchored to the floor. If you consider the arm is for example 2 feet long, then sitting on the extende seat will be the same as applying your full weight to a crowbar, two people sitting on one side would destroy a normally constructed island. Similarly, if fitted to a wall make sure that they are anchored well and that the wall structure is suitable. A nice idea to save space though

I can't really choose either as I much prefer the brushed metal than the chrome and would choose that - but if the other one is more comfy.... I had some black padded ones like the ones in your images (not quite as nice!) typical gas lift faux leather on a chrome base. Very comfy as lots of padding but the faux leather ones were super cheap - maybe £55 for a pair, haha. The chrome was awful and showed every bit of muck and dust and it rusted constantly. They ideally need sealing over with chrome to protect them. The faux pvc to me (even though I actually work with leather!) worked well as they were always getting grubby (especially when the nephews visited and put their dirty hands all over them, haha) and I had to scrub them down a lot so they endured quite a bit over the years I had them. The leather on the stools I imagine is similar to an upholstery leather so it will possibly look the same and not have that real leather feel to it (like some of the leather industrial style stools you find) and although I would always choose leather over pvc, if the seats are housing children then you might want to perhaps look at the cheaper end to start with to see how they get on with them. My nephews would spin on them, go up and down on them constantly, knock them over (rolls eyes) and needless to say, the gas lift started to fail on some of them.