First time trying to make a custom keyboard. What problems does this one have?

It's a split keyboard in 4 parts and 101 keys, though i could move the number pad and control pad to outside of the thumb keys if making a 4-piece keyboard is too hard or complicated.

Left thumb gets space, control, and super. Right gets space, hyper (just a 3rd layer), and alt. The keys next to T and N are repeat keys. Above Fn is escape and sleep. Above power is compose.

The control pad has cut, copy, paste, open, select all, save, undo, and redo.

I think that's every key i'll need, especially with a compose key and so much extra space available on the hyper layer.

Is there anything i've forgotten to consider? Anything i should know about split keyboards, or custom shapes in general?

More specific question, are 0.5u switches and caps available anywhere for all my small keys? I could replace most of them with full size keys fairly easily, but the 101st key on the number pad would make the layout asymmetrical.