You'll have to ditch the cardio once you start on the weights, intensive cardio anyway, otherwise you will just have to eat that much more to remain in the calorie surplus required to gain weight. Also, rest is a huge part of weight training, you'll be doing your body no favours running like a madman when you should be allowing it to rest, ie grow.Well that's why I need help. I want to eat more / weigh more but I don't want to put on much fat (hence the intensive cardio)
Gaining bodyfat is an accepted part of weight training, the idea is to get your diet and training in check so that you maximise the lean gains and minimise the fat gain. When the time comes, you deal with it.
Read this, it's a great starting point for anyone that wants to better understand some of the basic principles of weight training -
http://www.acaloriecounter.com/building-muscle.php