No finite answer here but, with beginners, I like 4 sets with timed intervals. Beginning clients need more rest to lower their heart rate and disperse lactate so the interval times are really client specific. The number of exercises are really goal specific so this is a tough question. the 1st set is not timed and I use it to orientate the client to the circuit (maybe 10-15 reps). I notice that it improves overall intensity for the next three sets with less postural deviations.