Okay, sounds like you're picking up some ideas.
As for the dropping of the bow arm, I may be able to help you. Usually this is caused by one or more things. One, you may not be aligned from your drawing elbow through bow hand. This requires muscle force to hold the bow in place. Two, you are trying to point or aim with your bow hand rather than your entire body and again requires muscle to hold in place. When you release the string, that force causes you to move your bow arm. Years ago, I figured something out on my own that has helped me a lot. Really I just transferred a principle from rifle shooting that says you should not be fighting to hold on target but that you should be aligned naturally with the target and all major support of the weapon should be from bone, not muscle.
What I found, was that if I closed my eyes and pulled my bow to anchor, natural tendencies were to align everything in such a way as to hold with the least effort. How does that help you shoot better? Well, try this. Do some practice draws with your eyes closed and strive to do as Gurn said and pull with your back muscles. There is a definite "push pull" effect. When you hit anchor you should feel rock solid. Bow arm is extended under pressure, (usually with just a slightly relaxed elbow) your other elbow and back are pulling string tension. Draw arm elbow through bow hand is a straight line. Do that several times to get a good feel for it.
Now, go out to your target and take your usual stance, close your eyes and with no thought of where the target is, draw to anchor and feel the "sweet spot". Now open your eyes and see where you are pointed. Probably won't be at the target. The trick is this. Your upper body learns to draw and hold to the "sweet spot" then you aim from the hips down. A good trad archer can turn in all sorts of ways and have his feet pointing the wrong place and still align his UPPER body with the target and get off a clean, accurate shot. What ends up happening (for me anyway) is that you learn to align your upper body with the target before and during the draw. If shooting down, you might bend your forward knee and bend at the hips a bit but YOUR BOW ARM THROUGH DRAW ELBOW STAYS ALIGNED. You don't just stand there and aim your bow arm lower. I'm sure you've heard it said to bend from the waist when shooting down out of a tree stand? Same principle but in this case you aim from the waist regardless of shooting down, up, left or right.
To verify, stand in front of your target and look at it. Now FEEL your upper body alignment and rotate your shoulders and torso left or right as needed, tilt forward or back for elevation, close your eyes and draw. Feel for that sweet spot and open your eyes. If you are dead on target you did it right but if you have to correct a little, your imagined alignment was pointing you in a different place than your natural alignment. When you find your sweet spot, open your eyes and are on target and release cleanly, you should find that your arrow flies true to the mark and NOTHING moves at the shot. Your bow arm will be solid because you were not pushing it around with muscles to get it on target. It was "just there" because your entire body was aligned. If you watch a good shooter their upper body and shoulders are like a compass that zero's in on the target just before they draw. It can be done amazingly fast and with little thought.
Another thing, never try to force your aim. Think of shooting your bow as almost a passive thing. All you do is line things up and observe the arrow on the way to the target. If you are trying to force your aim you will find yourself jerking at release or anticipating and releasing early. Just relax, line things up and calmly let the string slip away. It's a very fluid thing and should not feel like there is a strain or tenseness. That's partly what goes back to the need to learn with a lighter bow than you'd think you might need. If you are fighting the bow, it's difficult to learn the relaxed style of shooting. You can always build up strength and ability then shoot heavier bows but ya gotta be honest about what you can handle.
It's hard to explain so everyone "gets it" so I hope I didn't confuse you. Let me know if it helps.
By the way, if your equipment is not properly tuned and your arrows flying true, you will still have trouble but unless really mismatched, you should still see improvement in accuracy once your form and follow through get better.