I'm so glad to hear the little one with breathing issues is doing better.
Yes, being feisty is a good sign - that's just a baby squirrel for you
Oh when they open their eyes, then the fun really begins!
A cardboard box really isn't the best thing to keep them in as it can dry out their skin - I found this out the hard way with my first baby squirrel. A plastic bin like a big Rubbermaid storage tote works great for them, even after they open their eyes while they are learning motor skills. I prefer the clear bins so they can see out and I can watch them play.
Something like this works great, although it doesn't have to be that large.