Recommendation is 2 day between workouts. i vary between 2 or 3 depending on how much i have done previously. Some workouts warant long rest times.
Separate those muscles that work a secondary muscle so that they are far enough apart not to overtrain you. For example, do Chest Monday, triceps on Wednesdays, and shoulders Friday... and biceps Monday with chest, and back Wednesday or Friday
I prefer to stay clear of cable machines, as i feel that you are losing out from releasing the weights down, where free weights you have to control both movements.
I think you should add a few more sets of squats in there before a few of your other workouts, nothing to major,but thighs are very big muscles and need a bit more attention and are good for GH release.
Reps wise, anything over 12 you need to increase you weights.
8 is ment to be the optimum rep workout for gains, but that depends on what you want to acheive.
for instance you could do a workout like this
Week One is a power workout - Reps 4-6
Week Two is a strength workout - Reps 6-10
Week Three is an endurance workout - Reps 12-21
some people recommend doing 4-6 reps on 50% weight to give muscles a warm up after strecthing, followed by 8 reps on a weight which will allow you to only do 1 set, to the point where you cannot lift a single rep more.
i wouldnt start this straight away though, as you've only been training since january you get very quick gains, weight till you platue then change to this.
hope that helps.