Link the account with either Facebook or ATA ID. Not sure on android but on iPhone it's under settings(top left) then account. Hope this helps
That castle isn't as pointless as it may appear to you. Next to giving you access to the alchemist and later on the mage (oh joy), it gives you static stats. Those will help you avoid fails on ebs when you are low on troops, as a pot would do.
The mage brings you massive anger issues in exchange of some otherwise useless inferno and aqua. Well worth it !