Chapter 291 is out on one manga and manga fox manga volume and hut should follow suit
Currently in the manga series, hunter x hunter is in chapter 290 and is on hiatus. It is hard to predict when it will be out the manga or the new season, since (as the news say) Yoshihiro Togashi is...
I don't really understand what you said about "hunter x hunter piano" but there is a piano version of "Ohayou". (hunter x hunter opening)
Nope, and at this point, the chances are slim.
The Ryodan/Spiders (the same thing) Some people say it is Hisoka but he just wants a good fight with Gon