I've always lived a physically demanding lifestyle, with a job that requires a lot of heavy lifting, and a daily routine that has me walk 10 or more miles a day.

Well, now I have a cushy desk job, and I don't walk everywhere anymore because its just too far, so to stay in shape I'm probably going to start hitting the gym.

What would best emulate my old routine? I'll need to do a lot of cardio and lifting, so which machines should I use?

Yeah, go for it

I'm assuming you'll want to do endurance training in regards to lifting since your job probably required hours of it. That being said keep your weight low (not too low of course) and your reps high.
But as a guy who's been going to the gym for years, I can say that it'll take a lot of practice and experimentation to get your routine just right. I recommend doing as many free weights as you can and use machines for those muscle groups that are harder to focus on.