Nick, we can't tell you how much weight to use, we can, however, give you some basic tips to get you on the right track.
The amount of weight you should use (this has been beat to death, argued, debated, talked about, etc. but this is what I do, and I have gotten results) is figure out how much weight you need to use to reach muscle failure after the second or third set. Failure DOES NOT mean that you are unable to lift the weight at all. Failure means that you cannot perform the rep with good form.
Building muscle helps burn fat. Thats not debated anywhere. Any muscle you put on increases your basal metabolism. If you want to pack on some of the solid stuff, devise a routine that works the 5 muscle groups of your upper body (chest, lats, shoulders, triceps, biceps) and the lower body (glutes, quads, hamstrings, calves) Try to do 3 sets of 8-12 reps of each exercise. 3 exercises for the bigger body parts (chest, lats, quads, shoulders) 2 for the supporting muscles (tris, bis, hamstrings, calves).
This type of program has made me a lot more solid in the last 2 months. with a proper diet and a good routine, you will be happy with your results.