Well, I would probably just try to get a trainer/boxing club as soon as possible or whenever you get that time to fit it in. And since you dont really have any boxing experience you are going to want someone to show you how to do things and see if your technique and all that good stuff is correct. But if you dont know the techniques on the punches then I would be a little careful about hitting on the heavy bag cause the last thing you want to do is get into a bad habit or wrong techniques cause they are by far the worst thing to get rid of. But running, situps, pushups, (go to bodybuilding.com and get a lot of varations of the sit up like leg raises and air bike and all those are really good) are all great for you. Just do those until you get yourself a nice gym. And I guess if you really want to get into it, then its never to soon to start eating right. Have fun and welcome to the forum!

-Mike