Hi! I currently have 2 female mice but I'm wanting to add one more to make it a trio. My current set up is 26" x 18" which comes out to 468 square inches. Is 3 a good number for this bin? I've never had mice before and I don't want them to be over crowded. Also I currently have a 6.5" Kaytee Spinner. My mice aren't having any issues with it but I will probably upgrade it soon.