First and foremost, there’s a bajillion different pieces of advice people will give you - at the end of the day you have to do what works for you. Some of it is scientifically-based, and others are not. Nutrition is such a new science that there are new discoveries made all the time. I’d recommend making slight changes to your workout plan every three weeks so you can accurately monitor changes and see what works and doesn’t work. If you tack on 5 different changes and see results, you’ll have no idea if one, two, or all of the changes are helping you (or any possible combination).
I got decently big doing nothing but dumbbells (not by choice, I just didn’t have any other equipment at the time. I bulked up to about 225lbs at my max, but I was intaking about 5000-8000 calories a day. I hover at about 185lbs right now, and I prefer it more tbh. I look a lot cleaner, feel a lot better, and it’s a big confidence booster because I’ve never really had a six pack before I dropped down to my current weight. I work out typically every single day, but I revolve muscle groups so each group gets about 4 days off before fibers are again being torn again. Low weight high rep does next to nothing for me - I lost strength and did not lose fat (if low weight high rep = fat burner, every teenage boy would have cut as fuck forearms). If I want to build endurance more, I do medium weigh medium rep. But that’s just what works for me. You may experience better results doing something different.
As far as working out one muscle group more than the other, it’s dumb as fuck 80% of the time. The remaining 20% is okay in a few situations. Genetically, I have a big chest and my arms are normal. I would work out my arms slightly harder than my chest to start evening things out. Once appearance evened out, I started evening out my workouts. If you’re trying to do a particular exercise better, IE get a higher bench press, then yes you should bench more often. I’m currently trying to get back into doing 20 dead hang pull ups (not that gay ass CrossFit shit you see with people kipping and swinging their way to a pull-up) and finish off with one one-handed pull-up. It’s extremely difficult, but in order to get to that point I need to do more pull-ups and focus on back, shoulder, and hand (grip) strength the most right now. I wouldn’t recommend having more than one active goal in a particular workout, because it pulls too much focus away from the general aspect of working out. The last situation where it’s okay is your legs. Work. Out. Your. Legs. I don’t mean biking (although that’s great, don’t get me wrong), I mean legitimate protein synthesis. You release testosterone when you work out, and your legs are a gigantic muscle group. Work them out harder than any other body part, in my honest opinion - but also in an intelligent way so it’s not ridiculously disproportionate.
If you’re just getting into fitness I wouldn’t even worry about developing plans and whatnot yet. Getting into the gym is the biggest obstacle. You can walk into a gym and throw weights around like a fucking idiot (as long as you’re not hurting yourself) for the first few weeks and still benefit yourself because you’re doing shit that your body is not used to. Then slowly, over time, start developing plans and making subtle changes. Also, if you rely on carbohydrates for energy, do cardio after you lift. Lifting burns the storage of glucose in the liver, so when you switch to burning fat, it will be on the shit that will burn it quicker (assuming you go hard af on cardio).
Just my opinion, take away from it whatever you want. If you have any questions, feel free to ask. Good luck, welcome to the life.