I built a 5x5 a few years ago. It’s plenty of room for 2 adults. Too me, a 6x6 is too big in cases where you have to look multiple directions. You can’t see out every window from one position so you have too move more.

Build a 2x6 box to recess the windows.

I prefer trap doors. As long as you close them you can keep the rodents out easier.