Tracyree, nice coop! So pretty. I did the interiors of three of my coops with foil-backed foam insulation topped with either plywood or boatmakers' veneer (for my tiny coops). Did the floors of the smaller ones in vinyl, and caulked the heck out of all the interior edges with clear exterior caulk. I have been very happy with the insulated walls in winter, but I can tell you that retro-fitting insulation once everything is already built is NO FUN.
On later coops I always did it right from the start. The vinyl floors have been great, just make sure it's not cheap, thin vinyl if you do it. I even found some at Home Depot that looked like wood for the porch of one of my coops. My BYC pages have more info than you ever wanted to know.
The other thing I would recommend is ventilation, ventilation, ventilation. I cut holes near the roof and put in closeable vent registers. In the extreme heat of summer I have even bungeed a small box fan in front of one of them to suck hot air out of the coop and push it out through the vent. Old computer fans work well for this, too, and you can directly wire them to the coop.
And for mice . . . here it is a constant battle to keep them out. My rule is "no mercy." At the first sign of them, I start the snap traps - - aggressively - - every night until they come up in the mornings empty. Fig Newtons in snap traps have worked better on mice than any other thing I have every tried, but you have to stay on it quickly and consistently or they get out of hand really quickly. Mice are vectors for so many diseases that I just cannot afford to indulge my love for animals when it comes to them.
1newegg, nice birds! What a lovely color.
Oh geez, a huge cicada just landed on my kitchen window screen. They started up that awful racket yesterday. Ahhh May in Tennessee! Gotta love it. That thick sweet smell of honeysuckle in the evenings makes up for the sweltering heat and bugs, I guess. Tonight I can sit on my patio with the honeysuckle and roses, listening to the whippoorwill and enjoying that sweet time before the 'skeeters get really bad.
Enjoy the day, folks! Looks like it will be a hot one.