Toroidal: - What adjacent shapes will provide similar efficiency without technically being a toroid?
Hub: - Can we connect it to a "shaft" instead? - What about adding a gearbox in between?
Tip connection: - This specifically calls out connecting the tip of a leading propeller to a trailing body. This is where I'd probably focus first. Can you reverse it to connect a trailing propeller element to a leading element? Do you connect them back to the hub instead? What about a secondary/tertiary element?
Patents are more of a threat than a firm legal protection. A large company can tie up a small business in court until they're bankrupt, so it's really a matter of cost/benefit and how close you want to get to the fire you're playing with.