I'm so sorry to hear you were sick for that long. But it's good that you're well enough now to get to the gym.
Honestly, if I were your weight and height, I wouldn't go anywhere near cardio. You're very thin and the last thing you need to do is burn more calories because it sounds like you've got a very fast metabolism, especially if you stayed that thin while you were a couch potato.
I would focus on weight lifting, full body stuff, three times a week and eat more, especially more protein. Pre- and post-workout shakes can help you get more protein in your diet too.
I'd highly recommend Starting Strength as a lifting program since it sounds like you're a beginner. I've been doing it since August and I've never had better results with any other program. Here's a link on Amazon if you're interested http://www.amazon.com/Starting-Strength-3rd-Mark-Rippetoe/dp/0982522738
Typically, if it doesn't bother your stomach (it bother's mine), you want to do some whey protein about 30 mins to an hour before lifting.
Then right after you work out, you want something high in simple carbs with some protein. This will help refill your glycogen stores quickly after lifting. There are some products on the market that have this in a powder form you can just dissolve in water, like Optimum Nutrition 2:1:1 Recovery. They're kind of pricey, though. You could also try something like eating pretzels and having another whey protein shake. Another easy post-workout drink is good old-fashioned chocolate milk. The protein in the milk and the sugar from the chocolate is actually very close to the ideal ratio of carbs to protein.
If you find yourself gaining too much fat, then worry about cardio and cutting down on carbohydrates. But it sounds like you won't have an issue with that. Just make sure you're eating good food and not too much fast food and junk.
Hope that helps.