Under My Table, where is the option to save the table I've just created, so I can come back to it in the future and play without having to rebuild it?
I think more people would play custom tables if they were listed on the main Matching page also.
Not possible at the moment sorry.
You can save the kingdom like thins:
Village, Smithy, Gardens, ...
And copy paste it into "enter cards to include in your kingdon" to save time.
A workaround I use is this: before you leave the site, always start a new game with a bot/bots. When you come back, your table and game will still be there. If you wish to play humans, just resign the bot game -- it will not affect your rating in any way. HTH