As promised, here are some pictures of possible mouse holes. They're all fixed, so now it's just a matter of waiting and watching for signs of mice.
Now, if only I could patch up every box elder bug and Asian lady beetle hole. Sigh.
Photos below are a sink before & after and a pic of the gaping hole for bathroom access. I did convince Matt to just screw the board in place and not use crazy glue. Future access and all.