There's nothing wrong with a simple plan that hits the basic exercises three days a week. Starting Strength, Dan John's Southwood program, and plenty of 5x5 routines work on that principle. If your goal is to increase size and strength, that's the kind of approach that's worked for decades.
Don't think. Pick a pre-designed program and follow it to the letter. Almost any program on the site will be fine. Starting Strength (I disagree about the stalling. Nothing wrong with running it properly for a few months and then moving on. It's not a long-term plan), 5/3/1, the Southwood or 5x5 plans linked earlier, almost anything you stick with for 90 days and complement with enough calories to see weekly progress on the scale.
Yes, doing that much cardio will interfere with recovery and progress. You need to decide if you "like" doing that cardio more than you like building strength and gaining weight. I'd suggest limiting cardio to 1-2 hours a week, total. Your cardio conditioning won't wither away if you prioritize strength for a few months.
Are you still skinny/lean with definition? Just trying to get an idea of where you are, bodyfat-wise.
For a 6' tall, 160 pound guy to gain only 15 pounds in 18 months, I'd say you do not have a good handle on diet. Young, underweight guys can gain that much bodyweight in a fraction of the time it took you. So I need to ask... what, exactly, did you eat yesterday?
In the months you did the program (what's a couple, 2? 4?), how much bodyweight did you gain and how much did your strength progress in the squat, dead, bench, press, and clean?