I'm going to the gym 3 times a week (Mon, Wed, Fri) with the occasional extra day depending on work.
My goal is to lose some weight, not much, about 5-7 kgs (13 pounds?) and build some muscle.
I do 20-30 minutes of cardio, then weights, then finish with another 20 -30 of cardio.
Cardio is usually bike and/or treadles I think they are called. (Like a treadmill but with two 'planks' for each leg that move up and down as you step)
I believe with weights that the best way is to use heavy weight with low reps. Currently I'm doing 4 sets of 10, 9, 8 & 7, every main muscle like arms, chest, shoulders, legs, etc.
So, is this ok? Is a day inbetween sufficient time for the muscles to rest/rebuild? Is the cardio too much/little?

Thanks heaps.

Looks spot on to me. Make sure you hit all your muscle groups when you lift and make sure your diet is clean with enough protein and you'll be rocking it.