Keymaps in general are quite personal, so don't expect this to be the best keymap for you. It is however a good starting point for a keymap that works for you.
This keymap makes heavy use of keys behaving differently when tapped and held, so that all the keys one may need remain accessible despite the low number of thumb keys.
The Ferris keyboard is a 36 key keyboard with 2 thumb keys on each side, giving you all the normal letter keys on the 3 rows from the home row.
This keymap also uses homerow modifiers, which means that the modifiers are all on the home row. This is a very personal choice, but I find it very convenient. You can read more about homerow modifiers here: https://precondition.github.io/home-row-mods.
I also make use of Vim style navigation, which means that the navigation keys are all on the home row. Also in the browser I use Vimium, which is a plugin that allows you to navigate the browser using the same keys as in Vim. You can read more about Vimium here: https://vimium.github.io.
Just the qwerty layout, with homerow modifiers.
IN PROGRESS
On this layer I have all the numbers on the top row where you would expect them, and on the right keyboard I have a numpad with also the symbols that are commonly used with numbers such as +, -, /, *, =, etc.
On this layer I have all the symbols that are commonly used in programming languages, such as brackets, braces, semicolons, etc.
I placed them roughly where they would be on a qwerty keyboard, but I also placed some of the most used symbols on the homerow.
My 3rd thumb button is a MEH button, which means that it is a modifier that is active when held down. It is a combination of the modifiers ctrl, alt and shift.
I use this with Keyboard Meastro to create a lot of shortcuts. For example to switch between apps and to use a lot of functions in Visual Studio Code.
On this layer are the navigation keys.
On the home row on the right keyboard I have the arrow keys the same as Vim navigation keys. On the left keyboards the WASD keys are used to move the cursor around, with q and e being the left and right click.
I only use this mouse sparsely, but it is very convenient when you need to just quickly click something.
I am planning to add a touch pad to the keyboard, so that I don't have to use the mouse at all.