58F here with Osteopenia, so I can relate.

Heavy is different for everyone. But basically it's feeling almost maxed out at around 10th rep, and trying to get to 12 reps. As you do this on a regular basis you will have to continue to push yourself so the weight remains challenging. You should be focusing on the "push/pull" exercises: rows, bench press, TRX, leg press, squats, lunges. I lift 3 times a week, on the other days I go to barre which really helps me with balance and core strength. I also love walking. I live in a coastal town with a lot of hills and stairs. I just bought a 12 pound vest which I wear on my 5 mile walks up hills and stairs, and also on the sand - it literally kicks my butt.

Lastly if you listen to podcasts I love JJ Virgin's podcast, she is very relatable and she is very knowledgeable on all things nutrition and fitness - she had a recent episode that is on this very topic "Strength Training for Women Over 40 Made Easy | Ep. 586"
https://jjvirgin.com/main-podcasts/

Also look to join some Facebook groups focused on strength, like Caroline Girvan. Your plan is good, but you don’t need to focus heavy lifting for accessory muscles. You may risk injury with the smaller muscle groups. Strength for bone health should focus on large muscle groups with exercises like deadlifts, squats, bent over rows, overhead presses, bench presses. Caroline Girvan’s Iron series is a great place to start. Her programs are free on YouTube and there is also a Facebook group.

Why not get a trainer to help you learn?

Your plan sounds good. Here’s another one if you want variety.
https://www.washingtonpost.com/wellness/interactive/2023/strength-training-gym-workout/?itid=lk_inline_manual_38

I’ve done a fair bit of cardio but I’m a newbie when it comes to weights. My bones have weakened significantly in the past year, according to my DEXA, and my doctor is recommending heavy lifting. Not body weight or resistance exercises, but lifting. I don’t really know what that means. Nautilus? Free weights? How heavy is heavy?

My current workout is 20 minutes cardio and 30 minutes weight machines, rotating through biceps, abs, shoulders, triceps, delts, traps, glutes, calves, quads, and hamstrings. I choose a weight that’s moderately hard and do 10 reps. Then I increase the weight to where the last two of 10 reps are super hard but I can still do them with good form. Right now that means 40-60 lbs upper body and 70-85 lbs lower body.

Is this a good program? I’d benefit from a coach but I don’t have a budget for personal training. I go to a free rec center gym, so I can’t take classes. I’m reluctant to do free weights or videos at home because I don’t want to hurt myself or work incorrectly.