What a pretty nursery you're creating I think you're right that there is too much pink with the walls pink as well. I like the idea of offwhite/pale beige with crisp white on the skirts/architraves etc to pick up the furniture. A feature wall in a soft green would be nice too, it would balance out the pink so that it doesn't get tooo sweet.

Have fun, how exciting to have a pink bump after 4 boys