I give this a three because I have taken in animals before, but don't really have the backyard for it now. I have a nice, modest sized yard, but not big enough to do something like this. If I did, I wouldn't even have to think twice about it.

Already got one with stray cats in it...

This is a natural bi-product of planting a garden. This year, with my first garden, I met rabbits, lizards, yellow jackets , wasps, bumble bees, praying mantises, rabbits, worms, earwigs, lady bugs, ants, birds of all kinds...especially crows,  spiders of all kinds and a lot of Mexicans who saw the garden as they drove by and stopped to take a look. I learned how to made an ear-ringing salsa and we did a bit of trading, as they came back with some of their garden harvest. The rabbit-proof fence that I built also proved successful at keeping out the Cape Buffalo, crocodiles and rhinos...

Kinda depends.

Ideal species to create a backyard habitat for:
*Squirrels
*Birds
*Frogs

Not-so-ideal species to create a backyard habitat for:
*Bears
*Mountain Lions
*Africanized Honey Bees