could I just get some advice on simple ways to up the calories and the mass gain.[/quote]
A big breakfast, big lunch, and big dinner have gotten plenty of guys large. There’s absolutely no reason why it wouldn’t work for you. Add a protein-carb shake when you lift and you’ll be extra-golden.
Yes and no. It’s mostly a matter of priority. You’ll find a lot of guys, usually more experienced, who don’t go heavy and have learned how to get maximum stimulation out of a not-super-heavy weight.
On the flip side, there are guys who lift heavy and low-ish rep, but get a growth stimulus by bumping up the total volume - either doing more sets with that heavy weight or by doing lighter “bodybuilding stuff” after the heavy work.
For younger dudes still building a foundation, I’m not a fan of going super-heavy or going to failure (in any rep range). In that case, I’d say there’s not a ton of benefit going below 4 reps very often.