Have a look at MegSquats on Instagram & YouTube. I think she's great. There's a subscription programme with her as well, but I don't know about that.
The other Instagram account I follow is Achieve Fitness (Boston) - someone here recommended them & they are great! Lots of good videos on Insta about form & technique.
The two main lifts for going heavy that you can do on your own reasonably safely are
deadlifts
squats
But please, make sure you use correct form. I lift quite heavy & also do Body Pump & I see such bad form in pump classes.
The main fault I see is that people don't get the hip hinge properly at the start of a squat, and they let their head and chests go down with the squat. Squatting - you need to keep head up, and shoulders back, and stick your butt out, and put your weight in your heels.
It could be useful to do a few sessions with a PT at your gym, to learn correct lifting techniques.
And re the number of reps - I tend to do sets of 5 lifts if I"m going heavy. So an everyday training weight for me is usually around 60kg deadlift - 5 sets of 5 reps with about 2 minutes between each set. Or if I want to go a bit heavy, I'll just do sets of 3 at 70 or 75kg.
But only do that twice a week at most!