Doorbell installation without existing door bell

Yes the video doorbell needs power, wire size not sure but i know its spaghetti thin lol and voltage not sure as ss does not give that information out but i would look at what ever ring says because its got to be the same.

Doorbells normally need a transformer.  The wire size can be fairly small, depends some on length of run.

From Simplisafe doorbell info online:
From condo to castle, Doorbell Pro works.

Some video doorbells don't work very well with really old homes or really new homes. We custom built how our doorbell uses power, so it can work with almost any type of home or doorbell setup.

Works with 8-24VAC
Wedges for setup on shingles or corners