How often you weight train depends on whether you are doing total body weight training workouts each time or split routines, i.e. working just a few muscle groups intensely per workout.
If doing total body workouts, like Cathe's Muscle Endurance or Muscle Max, you could do these 2 or 3 times per week depending on result you see and degree of soreness. Two would be good for people new to Cathe.
After a couple of months, you can progress to 2 or 3 day split routines dividing the work up as follows:
2 day: 1 day lower body, 1 day upper body (example PUB and PLB)
3 day: 1 day lower body, 1 day chest/back, 1 day shoulders/biceps/triceps
If you do 2 day split routines and are getting into pretty good shape, you can choose to do upper and lower body once or twice each per week, or do lower body once and upper twice, or vice versa, depending upon what your body's needs are.
With 3 day splits, it can be hard to fit in working each muscle groups twice per week, time wise, given that you need to schedule 3-4 cardio session also, but it is indeed possible.
Re: Intensity series. You could do certain of the workouts twice per week, but do you have time to schedule each one twice? Don't forget that doing high impact cardio more than 4-5 times per week increases your chances for stress-related injury and burn out, and muscles do need time to recover in between workouts.
Clare
