If it is solely for your own use or distribution without any fee and you are willing to pay I don't see any conflict with the licencing (happy to hear contradictions).
That said,
(as long as it matches with my budget and expectation)
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leads me to suspect that your budget won't cover defining the specification much less the time to program and if required create artwork for such an untertaking.
Depending on what you are wanting, creating an entire custom UI is hundreds of hours worth of work even using existing addons.