That's fine as long as you allow for the electricity failing.

We have (inherited when we bought the house) 2 pumps in place. Primary is electric and does the day to day, backup is water powered.

Primary started acting a bit erratically so earlier in the year I replaced it with a new one. Took the time (and effort!) to connect it up using adjustable fittings, so can now swap out the electric pump in under 2 minutes. Old (erratic) one sits on the floor ready to go back into action if required. I do need to give the old one a good clean though

Definitely! Any backup device of any sort should be tested periodically.

Yes.

I had a whole post with photos of my basement for you and everything; just lost it all and the will to recreate it.