YC has funded multiple companies drone delivery companies - Volansi, Pyka, Flirtey, etc., and they've also funded a jetpack company (Jetpack Aviation). Being too ambitious or too difficult is not an issue, and if you want to apply to YC you should
My main concerns are applying without solutions for legal/physical scalability.
The fact that you know you need lawyers you can't currently afford is a good start because it shows you're at least thinking about the problem.