1) Start a weight lifting/progressive body weight program IMMEDIATELY (never too soon, before or after surgery).
2) Seriously, start now.
3) Lift heavy things often.
4) Did you see #1?
5) Find a hobby that keeps your hands busy (and makes it hard to eat). Preferably one that involves exercise. Specifically lifting heavy things regularly

Lol - sorry, but I wish someone how impressed upon me just how important this is. I lost 60 pounds, took "after" pictures and was horrified --- I was EXACTLY the same shape as I was before, just in a smaller version. It was like someone used a shrink ray on me - no change in fat distribution, overall shape etc. I evenly "shrunk" everywhere, so I was just a smaller lighter fat person. Weight lifting not only helped me lose more weight, more steadily (but slower), but I got to eat more-permanently, with much fewer aches/pains, get out more, be more active, stronger, healthier etc. And the shape changes were DRAMATIC. Finally, I look like I actually have a "real" shape, rather than the "weeble" look I was rocking before.

Heavy means heavy for you! Basically start very small - even with nothing at all. Do 8 reps concentrating on the muscle contracting both on the way up and down. Rest one or two minutes. Do it again, total of maybe 3 times. If that turned out to be pretty easy and you feel like you can do more, next time add a little more weight. Every time, increase the weight until you have to struggle to finish that last set of 8. Stay there until you feel like that was pretty easy and not a struggle, then up it again!

The actual weight means nothing. It is the continual progression that is very important.

A good starting place would be to google "Joyce Vedral". She started weight lifting in her 60s I think! She is probably close to 80 now, but kept making videos into her 70s for sure. She also responds to emails (at least a few years ago!). Her videos (and books) are not as polished as some, but she is definitely inspirational

Also important, once you get going, is balance... Make sure you dont overdo one thing - i.e. always doing biceps but not triceps. General rule is - if you can push 10 pounds, you should be able to pull 10 pounds... So always work opposing muscles fairly evenly. Otherwise you end up with some skeletal issues that cause pains and chiropractor type stuff!

Getting started is most important, then keep learning and adjusting as you figure things out and read more and more!

Good luck! It really is lifechanging. Very slow, but consistency really, really, really pays off. Take lots of pics on the way!

Heavy is what is heavy for you. It's going to vary person-to-person, so there is no set number. The sort of general rule is 12-15 reps = light weight
8-12 reps = moderate weight
5-8 reps = heavy

You want to make sure you're progressing. I would recommend looking into a weight lifting program, like New Rules of Lifting for Women or Starting Strength. There are books for both of these that detail the programs, and there are also groups on here that can answer any questions you may have. There are body weight programs out there too. You Are Your Own Gym is a good one (and has a book for reference).