If you put your Musks into a pond that size you will never see them! They are really quite shy, secretive little things and will be totally lost.
That said, your pond sounds ideal if you were able to take on some large sized Sliders or Cooters that desperately need rehoming. I'm sure we could put you in touch with someone that knows of some that need rehoming.
Romski on here lives rougly in your neck of the woods and has some lovely natural pond setups. Put his name into the Search facilty and go to the threads or posts by him (apologies if you know that already) and has lots of advice and info about overwintering turtles.
Ours are outside during the warmer months but return inside from October to April.