1. to avoid "Failed to apply patch. Please try again later. " error you just need to log in using your Warmane account name, not email address.
That is it
3. to avoid being stuck on " Authenticating" you need to do this:
1) Restart your PC
2) close your Torrent client and move your WoW folder away from your Torrent's download destination
3) now right click on WoW folder> Properties> remove "read-only"
Btw:
Lordaeron: it is x1 realm with harder pve content (Bosses of Wotlk raids have more hp, more dmg and shorter berserker timer). It was a "progressive realm" but, since it has bene launched on september 2015, it is stacked at ICC-RS since many years
(no gear on Coins-Shop)
Frostmourne: is a "progressive-seasonal" realm. Which means every year it get resetted for a fresh new start. It emulate 3.0 patch and progress to next the patch every 3 months
Icecrown: it is the older realm, since it is the result of the merge of Deathwing+Ragnaros realms. (that is why is the most populated, it is stuck at ICC-RS since always)
Blackrock: it is the old Wotlk-Arena Torunamnet realm . Instant max lvl, only pvp. You can do Duels, BGs, Arenas (you will face enemy from icecrown/lordaeron as well in bg/arena)