Q1: You are way overthinking this. Just go to the gym, work up to a set of 5 reps that feels moderately heavy. Do that weight for 3 sets of 5. Next session you add weight. Its better to start a little too light, rather than too heavy.
Q2: As I told you in the other thread, Id be very careful with adding anything to the program. You dont need to do anything else for triceps as youre already pressing three times a week. If you worry so much about your precious guns, do three sets of barbell curls once a week, after the main workout. But frankly, this should not be your main focus at this point. For now, the best thing you can do is to get brutally strong on the basics.
Q3: Find out what works for you. What works for someone else might not work for you. Youll be squatting 3 times a week, that gives you plenty of opportunity to experiment with your form.
Q4: Stop overthinking. Eat lots of whole foods. Dont eat too much crap. If you want to gain weight, jump on the scale once every two weeks. If the scale is moving upwards, keep doing what youre doing. If not, eat a little more.
Right now youre way over analyzing everything. Once you get your ass off the computer and into the gym all these things will fall into place and youll stop asking questions like this. Good luck, let me know how it goes.