How does one become a hermit and do they where any sort of habit? Like a cassock?
Depends on the type of hermit. You could start with looking at orders that have them like the OSB cams (contemplation.com).
What about urban hermits who live in cities?
My suggestion was to start with this group (I have a friend who is one at the monestary at Big Sur) - they could guide you and I believe they have some who live in urban settings.
You have to start somewhere - get a bit of chat going with them and maybe you can find some referrals and help to fine tune your inquiry.