Taking down walls and insulating the addition

The house we bought has an addition. We took down the paneling on the side attached to the old part of the house. There are wood planks and if you look through the gaps, there is are wood planks laid on top of concrete (I.e plank, concrete, plank, concrete) all the way up the wall. Is that normal? I have photos if there is a way to attach them. Would it be hard to take that wall out?

My other question is: on the outdoors side of the room, they have old insulation and behind that some sort of felt. I'm not sure what the felt is for. There are also 2x4s nailed horizontally in between each stud near the top of the wall... About 6 inches from the ceiling. I also have photos of those - I was wondering if they could be removed or if they serve a purpose.

Thanks
Brianna