For most of my life I was underweight and had trouble packing on weight and muscle... until I discovered protein powders. The difference was dramatic once I started adding protein shakes into my diet, even though I thought I had a decent amount of intake through eggs and meat at most meals.
I'm not at all schooled on the dietary side of things, any suggestions on reading or basic information to keep on hand as a rule of thumb?
These days I just try to have 2 vegan protein shakes a day (way less distress for the digestive tract than Whey/Milk i've used) in the mornings and after workouts.
There is no free lunch. Medically speaking, "protein heavy" diets are bad for you. They stress the kidneys and increase the chances of various forms of cancer. Really, what you are doing is trying to tow a trailer with a corvette, when you treat your body this way. The human body was not meant to bench press its weight for reps, or squat twice its weight, or run marathons, or any other matrix you have for performance.
But we want extra performance...we crave it. Sometimes, professionally, we NEED it.
I was a "hard gainer", as well. I still am. Some people are genetically just not going to be monsters. This leaves you with two options...juice...or accept it.
That said, a lot of people view me as "big". I personally, do not. I am 195# and 5'10.5". Deadlift 315 for reps, squat 275 full ROM for reps, currently worked my way up to the 100# dumbells on the flat bench for reps. So I'm not a complete noodle, either, I guess. However, you, OP, may very well be a lot more robust than I am. Dunno. So take my advice with a grain of salt and don't roll your eyes too much at the little guy, if that's the case!
My advice is to eat 500 kCal more than you burn, and stick to about a 65% carb, 20% protein, 15% fat diet. This should not stress your system, and should be sustainable. You should be able to get this from a PROPER diet. Slacking on your diet? Get your protein from shakes. Cheat on protein...NOT carbs. Carbs need to be proper and complex. Sweet potatoes. Whole-grain cereals. Brown rice. That sort of thing. A "loose" Paleo (google it for more info than I know) diet is extremely sustainable and healthy.
You don't sound like a pro lifter to me. These are the guys slamming 1.5g protein/body weight pound. They are hitting the needle, and doing massive amounts of lifting every day, and need it. You, I presume, are not in that category. All those magazines you read are written by guys like this, or for guys like this, or about guys like this. They aren't written with people like US in mind, typically. As far as a training schedule, man, that is so personal I don't know where to start. Some people do upper/lower splits, some people isolate body parts, some people do compound lifts only.
My philosophy is a whole-body/whole performance one. I got into weight lifting because I got into fighting. I needed speed, stamina, and power. To get that, I do plenty of cardio, and I do complex/compound lifts like dead-lifts and squats, along with isolated lifts, like leg extensions and leg curls. Also, lets not lie, "pretty muscle" gets the ladies going, so yes, I do also perform isolation curls and the like. However, when I would lift back in college, I rubbed elboes with Kendrick Farris (Google him if you want, multiple Olympic medalist, powerlifter). The guy was about 183# and 5'7ish when I met him. He was shredded. He was clean and pressing 215kg. Not lb. KG! He was a damn monster. He simply did complex lifts. He looked just like he sounds---beastly and shredded. I never saw him doing isolation curls. The closest I saw him come to "training a body part" was playing around on the bench. For those guys though, they got arms and everything else from big, complex lifts. My shoulders bother me when I do a clean and press, so I don't. If you can PROPERLY DO ONE, I suggest the clean and press as the best lift of all time. If you can't properly do one...then learn to, or don't do it.
DO NOT SACRIFICE FORM TO HIT A LIFT! (with exceptions).
If you sacrifice form, you WILL HURT YOURSELF when you get to the big boy weights. I ended up giving myself a grade I/II shoulder separation. I got off light, but it took me outo f the gym for a year almost.
The exceptions here are "cheap" lifts, such as not going full ROM on a squat when "learning" the feel of a heavier weight, or "slinging" (in a controlled manner) or not going full ROM on a curl, to get the last 1 or two done in the set that you otherwise wouldh ave not even attempted. Cheating is okay...if you cheat SMART! But cheating because you are lifting too heavy, or don't know how to performt he lift will bite you in the arse every time.
Just my .02
Building Block Lifts:
Deadlift
Squat
Pull-up (over-hand and under-hand. I do under on arm days, over on back days)
Bench press
Over-head press (I prefer dumbells for all of my lifts but squats and deadlifts)
If you are beastly in all of these...you've got it made. The rest is just filling in gaps, having fun, and/or looking pretty or correcting symmetry issues.