For your tank... I'm assuming you meant which race should you be, not which class, since you seem to want to be a warrior! Well, if you were Horde side I'd recommend Tauren for the health buff. But honestly, I *never* pick a race based on the racial features - only based on the flavor. If you are going Alliance side, I am quite partial to dwarf warriors myself but pick whatever seems most fun to you!
Heirloom experience should be boosted, now that zones scale. If a zone scales along with me, it shouldn't matter if it gives me 20 levels instead of 10. I'm still enjoying the experience, even as a veteran player. I don't need to see every zone on every character again; that's the point of heirlooms. I can still enjoy the leveling experience, and the scaling, and the full outdoor experience of the zones -- and still get to the end game content I enjoy in a somewhat reasonable time as an employed adult. And the change wouldn't affect new players.
Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.