No problem bro
1: You are confusing the brachialis with the brachoradialis. The former runs underneath the bicep brachii crossing the elbow. The latter is a forearm muscle used primarily in wrist extension and gripping.
2: Spot injection protocols, when used appropriately can be very safe and effective. think of it as a very anabolic form of localized fascia stretching.
3: Sissy squats are great done with or without weight depending on your stretngth, sets, reps, and fatigue levels. i personally usually hold a dumbell in my off hand or hold a 45 lb plate across my chest.
4: Its tough to overtrain the abs. there are so many muscles around the abdominal wall you can use to compensate generally when the abs are fried other muscles will help them out.