I'm moving to a new house and their is a pond in my backyard. It's not to big but perfect size for a turtle.

1. Does a turtle need a partner to be happy?
2. Does the pond attract frogs?
3.If a turtle can't live their, a koi fish can fit, do they also need partners?

yes turtles can live outside unless its not a baby and you have to make sure no wild animals will hurt it

1. You do not need to provide a partner, it will be fine on its own.
2. The pond will naturally gain frogs yes.
3. You would normally put more than one koi in a pond and they will be fine wither females or males.

The pond must be deep enough for a turtle to hibernate. Naturally a turtle will burrow in the mud as they do live in cold climates. What species of turtle? This is important. If it is a native species to a cold winter climate it will do fine.

yes they can live outside