Looks good.
I'd be interested in both the regular and f-row extension kits, but I think putting either in the base would unnecessarily bloat the price. If anything, numpad should go in base.
Only other thing is to reconsider the colours of the 4-key 40% keys in the base kit. On most 40% boards 'esc' is R2 (adjacent to Q), 'tab' is R3 (adjacent to A), and 'backspace' is R2 (adjacent to P). Backspace and esc could probably go either way but keeping the tab in the light beige would look weird as it would be one row down from the rest of the light beige keys.