Designer Athletes is obviously a great program to use. Only you can determine if it is too much volume- everybody has a different work capacity. One of the best signs of overtraining is the inability to go to sleep. A good workout during the day should wear you out and help you go right too sleep. If you are overtraining it will be the opposite- you will be very tired but unable to go to sleep.
Scapular wall slides are pictured in the article. There is a picture of prone cobras in an article somewhere on here. Use the search function. I find often those types of activation drills just require a little practice. If you have a more specific quesiton on how to perform a movement ask Mike in the “Author’s Locker Room.”