Q. Can you do any glitches?
A. Of course you can! Every game has to have at least one glitch.
There is one non-damaging glitch, called 'Stolen Poke ball glitch' [here], if you're interested. Otherwise, you can search the internet. :3
Q. Will there be a Shiny Volcanion?
A. This can't be confirmed yet, there might be though, I dunno. Where not gonna get anything out of Nintendo since their existence was leaked, rather than announced.
Q. Are Xerneas and Yveltal shiny locked?
A. Well, yeah. They kind of are. No one on the internet has found a shiny legendary of them yet, especially since the shiny rate has risen, so there's a 99.99% chance their shiny locked, sorry.
Source: The many sites I briefly looked through that stated they haven't found a shiny yet
Q. Is there a limit to the amount of clothing you can buy?
A. I highly doubt there is.
Hope I helped. :)