Ok, long distance travel in WoW is a problem, especially at low levels when you discover a quest that takes you across the continent. And long Flight Paths are definitely a thing (think only being able to travel by Porter). But that's a design decision you, and everyone has to decide how important it is to them. I think of it as a chance to use the bathroom.

Bags yes. Fortunately on most servers, bags are cheap - they've made it among the first things you get in the latest expansion with tailoring, so everyone makes lots of bags. The intro quest (which I think the demo takes you through) leaves you with 4 10-slot bags, which is usually enough for a low level character.

And while you can't transfer items (in most cases) between Horde and Alliance characters, the Auction House has been shared for a few expansions now. So that's a lot less of an issue.

WoW is similar enough to FF that you'll be able to play nearly immediately. The combat system will take the greatest getting used to - the global cooldown in WoW is a lot less than in FF. Combat moves *much* faster, and there's less telegraphing of blows.

what it really comes down to is a style thing. Go in with an open mind. You may find that you prefer some of WoW's design choices. And also keep in mind that the game has evolved over 17 years, and they have not retroactively fixed everything, so there are continuity issues, and you may be confused about the overall plot when you start from scratch. It's up to everyone to decide for themself.