You can search: https://museapp.com/handbook#to-search -- but you're right this isn't our main focus, the way it is for something like https://mymind.com/ . What we've seen from the year of beta testing is that our spatial memories are very powerful and even users with huge corpuses navigate rather than search.

Yes, boards and cards are a key abstraction. Boards are just a type of card that can contain other boards--think of boards like folders/directories on a filesystem.