for overall fitness go for sets of 60 - 120secs over reps, resting of you need to and re starting until the time is up...this is just a thought though...
basically for strength use sets of 3 - 5 x 5 - 3 sets...for muscle/fat loss use sets of 10 x 3 - 5 sets
your aim is to be out of breathe anf feeling a lot of lactic acid build up...try not to rest even when you want to until the circuit is finished...
also perform the exercises in a different order each circuit or session but that may depend on what wts you have as you don't want to be changing them in btw sets
The page has some info you may find useful. It has a video tutorial of various exercises, disadvantages and advantages of training, plus exercise descriptions: Circuit training
2mins maximum should do then for deads and 40secs for plank...be sure tio increase plank holding time though, 5secs per session should be alright until at 2mins straight