1. 8.5/10 FFX has, imo, the second best OST of the FF series. And To Zanarkand is my third favorite track in the game (after Seymour Battle and Someday the Dream Will End), it's a beautiful piece for sure.
2. 8/10 it's been a while since I played Xenosaga Episode I, but I remember liking this track.
6/10 I did appreciate the route themes more in the remake than I did in the original GSC, that said I still like the original Route 29 theme a bit more. Especially since it's faster paced compared to this one.
8.5/10 when the description said it was a mashup I was kind of wary at first, since oftentimes game music mashups I come across don't mesh well together (especially if it's remixes, official or otherwise), but I think this is one of those cases where the end result is actually pretty great.