I love the leg press. Vary your feet width and height on the platform and be sure to keep your ass in the seat. Focus more on reps than the amount of weight. Too many guys really ego lift with the leg press with quarter movements. No bueno!

Justin good question and glad you're trying the single arm rows though I want to be clear because I think the video may have given you the wrong takeaway. Don't interpret the arm rows as the only thing you need for a complete back. I was saying it's the single best exercise for back development and if I was to pick one, thats what I would do. One exercise alone is not enough to build a full thick back. Here's how I'd structure it in your upper lower split running twice a week. On your first upper day make single arm dumbbell rows your primary back movement. 4 sets of 12 to 16 reps taken to failure on that last set. Slow controlled reps with a hard squeeze at the top. Then follow it with a vertical pull like lat pulldowns for 3 to 4 sets same rep range. That gives you both a horizontal pull and a vertical pull which hits the back from two different angles. You need both. On your second upper day you can repeat the single arm rows or swap in a chest supported row to take the lower back out of it. Then add a different vertical pull like close grip pulldowns or straight arm pulldowns. This way you're hitting back twice a week with enough variety to stimulate real growth without overdoing it. 4 sets of 14 is fine on the rows but make sure that last set is a war. If you're stopping at 14 and could have done 18 the weight is too light or you're not pushing hard enough. That last rep should be everything you've got with perfect form. Post a video of your rows in here and I'll check your form. That alone could be the difference between the exercise working and just going through the motions.

Sounds like you’re dialing in and I like the split idea. Regarding arms, especially if you have good arms, once a week is fine. You end up working arms with other body parts anyway. On the leg side if you’re solely limited with dumbbells definitely do the rdls, I love them. Add some type of wedge to the floor so your heals are elevated a little for more of a stretch. Goblets, Bulgarians, basic squats with dumbbells on side can all work the legs. Try to get at least 12-14 sets in per session.