You seem to know bikes so what you get is up to you. I will state that getting back in shape takes a long time. Less so with your age but still we're talking about at least a year maybe 2 or 3. So the first thing to work on is getting consistent. I think the biggest mistake people do when starting out is going too hard too often. Eventually it becomes just too painful and they quit. So I tell people to hold themselves back. Get off the bike feeling like you could have gone farther.