You can read about the us military training standards for ruck marches, and there’s military forums where they talk about it and give advice as well. 60 lbs would be towards the upper end so that’s plenty of weight, especially if you’re just power walking. I wouldn’t recommend jogging very often with the ruck (at any weight) because a lot of people get too much bad wear and tear on their body from that. speed walking with good form is very low impact on the joints and fine for training, and then just do regular jogging to bolster your cardio (which you would be doing anyways). Core training is also important because it keeps your body solid and allows efficient transfer of force from your shoulders/arms to your legs and vice versa.

By frame I just mean any rigid frame. Basically you have the solid frame which goes on your back, and then the sack hangs off of the frame. If you look around you’ll see what I mean. Some frames are internal and some are external. The hip pad is important so the weight can be shifted to your hips and doesn’t all just hang off your shoulders.
I think a lot of modern frames are made of plastic (or “high impact polymer”) but those have been battle tested so I guess they’re fine.