General questions
It is an Android app that allows you scan an area to find Pokemon
No, PokeAlert does this for you. Remember don't ever log-in with your "dummy" accounts on the same phone as your "main" account. Note that log-in PokemonGO on an other device is safe
Due to many security restriction put in place by Niantic, 1 account can only make 1 request every 10 seconds... This is why PokeAlert allows you to add more than only 1 account
PokeAlert produce very good result with only 5 accounts on a radius of 500m. But then again it will depends of your need. The more big the radius the more account you will need so that scan complete in a decent amount of time. The majority of PokeAlert user uses between 5 and 10 accounts and thisis plenty enough for a fun hunting tim around you.
Again because of security measures you cannot start and stop scan in different locations. If you start a scan to far from where you stopped it your accounts will be "speedlimited" and will NOT show any Pokemon for a limited amount of time.

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