10 lb. = 1" arm gain is a general, useful guideline-no one said it's exact but it holds in general from my experience, has nothing to do with arm size in relation to final actual bodyweight-we're talking a good general rule on rate of future gains if training hard, eating well and gaining mostly muscle. Those 150 lb. guys with good arms would probably agree with the 10 lb. rule when they were building up, actually.
Re: overtraining, it isn't that complicated-arms need somewhat less sets than larger muscles, but the rest needed is the same IMO; experiment with different rest periods for each muscle if this matters to you. Bis/tris anywhere from 5-9 tough sets going to failure and sometimes beyond vs. sets in the low-mid teens for torso and legs. Basic size builders are dumbbell/barbell/cable preacher or standing curls, it's that simple. Hammers are mainly going to effect forearms and lower bi tie-in to the forearms, isn't the best for overall bi development.
Bench dips in my experience are vastly better for tris than regular dips in terms of isolation as well as significantly lower shoulder stress. Hang a dumbbell between the thighs or use resistance bands.
For lower chest decline dips & flys are just as good as dips, experiment with the angle of decline and see which works better for you.
French Press is another term for lying or standing triceps extensions. The more confusing term is skull crushers (weight brought down to the forehead) vs. extensions, to behind the head (far more effective, skull crushers are sh-- re: muscle stimulation and should be re-named elbow crushers for the stress put on elbows). Extensions are the single best tricep size builder, IMO.