Where are your legs? When do you hit triceps. Why don't you list in your split where you place legs, tri's and bi's?
You just answered your own question: you treat arm work casually. Dedicated bodybuilders do not refer to training as "some work"; they have a specific day they work biceps, as in a "biceps workout".
You're also inconsistent with triceps. OF COURSE you will be somewhat fatigued after working chest. This doesn't mean one should ditch triceps work! You will be more and more fatigued as the workout progresses regardless of what body parts or exercises you are hitting! That's like a bodybuilder saying he is not going to work hamstrings after quads because squats fatigued his hams (and they do!).
False. Unless doing pre-exhaust, isolation work is hit after the bigger lifts. Considering not everyone does pre-exhaust nearly all isolation work is done after the big lifts. Uhhh, ask several Mr. O's and even impressive gym
Then work triceps and biceps with other bodyparts instead of having an arm day.
No one overtrains from adding a few sets of a forearm exercise or working their triceps. Sorry, you need a whole lot of OVERALL training for this to happen!
Dude, I am not saying this to be a jerk, but you have no grasp/understanding on training generally, which is clear from your post. You likely have little muscle mass at this point and should really educate yourself on bodybuilding training with the thousands of articles on this site.