I am considering this app as follows.
Animals will need some physical identification tag (qr code, or rfid). I think we need 3 screens
1. Login/Sign up/Forgot password
2. Add new / Edit tag
3. Add new / Edit animal
Further operations may be much specific to your use-case. May be, scanning an animal's tag, for instance. I don't know what you want it to do exactly, so considering a couple of screens for such operations.
So, it's 5 / 6 screens,
Firebase,
and may be a small and simple API (either in php or node, I will recommend php over node if you expect large traffic).
Also the mobile app UI/UX.
I think I can pull it off. :)
And yes,
(45+90) is (135).
Thank you.