Welcome, and congratulations for taking the first step!
I only have a couple of pieces of advise to start with:
1) There are a ton of programs out there, and all of them will help you, depending on what your ultimate goals are... As a beginner, pretty much anything you do will get you stronger and healthier, at least for a while. I personally do 5/3/1 by Jim Wendler, which I like because it's built on slow, steady progress, which is good for an old guy, but that's far from the only option. Do an archive trawl of T-Nation articles and you can find a ton of different programs. Pick one that looks like it fits your goals, and stick with it for 6 months before you decide something else you read looks like it's better. Starting Strength will probably get you through about 4 months before you run out of newbie gains. Don't let training ADHD get you.
2) Start slow, both with your diet and with your exercise. It's easy to make a commitment in the moment to suddenly do everything better and drop all your old bad habits, but real life seldom turns out that cleanly. Making commitments is definitely a good first step, but there is danger in an all-or-nothing approach, and it's easy to just abandon all your good work if you have a bad day or bad week, fall off the wagon, and decide it's not worth it, or you can't do it, you're not strong enough, or whatever. Accept that you will make mistakes, and plan on them so when they happen they don't derail you. As far as protein goes, 1 g/lb of lean body mass is a good thumb rule.
3) Have fun! Don't be discouraged when progress is slow, just be consistent and change will come.
4) One more thing - since you're totally new to this, I would suggest finding a trainer to teach you to lift safely if you have the means. You can learn a lot from watching videos and reading articles, and the Starting Strength book (you bought it, right?) does a good job of showing the mechanics, but nothing replaces some hands-on coaching starting out. I don't know if I'd do the GOMAD though, since you're trying to lose weight...