Firstly, how does one “raid” another farm/ranch? I'm a bit confused about how that's done.

Secondly, does anyone know what the rules are for having more than 1 account, or stables? Can I move horses between my stables if I need to, or want to move specific horses to my other facility? Thanks for the help!

For raid you have to go to a participant's stable page, then click the events and games tab. Then you'll see the option to raid.

Your accounts must be played entirely separately, so no you can't transfer horses between accounts.

Thank you Eyrie