After reading your entire thread, here are a few thoughts and suggestions:
Exercises—add push ups to your program for the back of your shoulders. In the spring and summer, kayaking is also good for the back of your shoulders and gets you off a baseball field for a while. Squats are good, but try to do a lot of one-legged squats or jump squats to build strong hips and glutes. Zita points out that the hips are the link between the upper and lower half. Not only will it help with energy transfer, but it also helps with balance, which is a key ingredient to a smooth and efficient delivery. Fearsomefour also makes a great point about energy directed forward and not upward. I’ve seen a coach put resistance bands around the pitcher’s waist and have them drive away down the mound while they held the other end to try to get them to feel the best way to put pressure on the band. I haven’t tried it myself, but I was intrigued.
Based on your height and weight, it would be beneficial to put on a bit of weight, but be sure to strictly maintain full range of motion. Power and explosiveness points people in the direction of heavy weights, but exercises and work outs that are lower weight and high reps will help maintain range of motion.
I’m not sure if you are still working on the treadmill, but don’t forget about your sprints. A long run can be mentally refreshing, but the sprints will translate better to mound work which is repeated, explosive effort.
Nutrition—LOL about the muscle milk. My son keeps snack bags of peanuts, almonds, M&Ms and raisins that he mixes at home and he doesn’t use anything that comes in a tub or bucket that has a picture of a muscle-bound, vein-popping weight lifter trying to convince him that the photo is due to the product and not to the steroid injections. Stay away from energy drinks if possible and definitely those high in sugars.
Catch—try to play catch with someone who throws harder than you do. Your brother may not be as good as you due to age and work ethic, but maybe some of your mental side will rub off and benefit him. You can work on your accuracy with him. Try to pick out a spot on him and hit it. If he comes to love baseball like you do, it will be worth your time.
Shagging Flies—great way to get some sprint work in if the guy with the fungo knows what how to handle it and enjoys torturing people by running them left to right and forward and back.
Long toss—you mention long toss. How long is long? Do you prefer flat to small hump distances or long arcing for max distance?
Solo work—is a fact when you are in High School. The key is to have that solo work be meaningful and transferable to game situations. Try to get a partner or a core group of team leaders to practice with and work out with. Don’t get depressed if you can’t get huge participation or buy-in from some team mates. Many of the kids are involved in several extra activities and baseball is just one among many. Also, HS is time for a bit more social interaction. Don’t miss the experience of HS to get an extra BP—especially if you are getting work in 5 days a week. You should have 1 or 2 days a week where you don’t touch baseball equipment. For example, my son really enjoys going to the HS swimming pool. Now he is on the swim team in the fall and winter months.
You may want to get that bucket of balls and try some pick off moves to a net. Weave some rope in the form of a square into the netting or use some athletic tape and start working on a killer move. It’s something that teams don’t spend a lot of time on, but can really help you control the running game. Your catcher will appreciate the effort you put into keeping runners close at first.
Pitches—you mentioned long fingers. Change-ups and your 2 seam should get some good movement on them. You also have a curve and 4 seam. How’s your cutter coming along? Do you have an ‘out’ pitch or a ‘go to’ pitch? It’s helpful to have a non-fastball pitch to throw in hitter’s counts where they may be sitting fastball.
Batting—tee work is great for working on swing mechanics and getting the feel for hitting the ball in different spots. Just be sure you set the contact point of the ball up properly. Remember that when pulling the ball your contact point is actually out in front of the plate and when going oppo, the ball is more over the plate. I see many people set the ball up on the outside front corner and try to drive it to right. That position is more of a defensive slash to right. Soft toss…I’m not a big proponent of that, but if you think it helps you, go for it. My practices are NO SOFT TOSS zones. We use reduced flight balls pitched from in front at the proper trajectory and reaction times consistent with what is found in a game. After two weeks with no soft toss and only hitting a ball coming straight at my kids, they all hit better than when they used soft toss—just saying Fearsome also made a good point about spending money on cage time or lessons rather than going to showcases unless you are a top player.
Travel ball—an expensive way to get discriminated against if you do not share a last name with one of the coaches. If you are going to play travel ball, and can afford it, try to get on a team that pays their coach. If they aren’t successful they will be gone. They have to play their talent.
Scrimmages—absolutely love them. They are a great way to evaluate personnel and get great information on the other team. Make notes, charts, whatever. Knowing your enemy is halfway to victory. I also love inter-squad and situational practices with live pitching.
Got any recent video or a Youtube channel with some recent pens or game video?