Re: crit vs circuit, the biggest thing is that if you flat or crash on a circuit you don't get a free lap. Basically it's more like a road race in that sense - if you come off the back You're On Your Own (aka "YOYO").
For any loop that has a hill you're going to be dealing with zero elevation change every lap, meaning you end up exactly where you started, and within a few minutes of racing. This means that the hills aren't as crazy as in a RR (no 35 minute climbs) and there's a pretty long downward slope somewhere (because most courses with a hill will put the steep grade as an uphill, not as a downhill, and the shallow grade will therefore be a downhill).
This means it's a classic sprint-recover type of effort. You go hard up the hill and over the top, you soft pedal and try to recover, then you do it again. If you can recover quick enough then you can do this for a while. It's a harmonic rhythm type thing. If recovering takes you 30 seconds and the next effort hits you at 25 seconds then you'll get shelled. If the effort hits you at 35 seconds then you'll be uncomfortable but able to hang on. 60 seconds and you'll be golden.
If you find yourself on the good side of the effort-recovery cycle then you should try to improve your position by extending your effort a bit longer. Usually it's more beneficial to keep going over the top of a hill (climb "through the top" of a climb) rather than starting your effort just before the hill. The delta in effort versus the benefit is usually better if you push after the climb, not before it.
To make this work you have to be able to draft well. You can't drift back into the very back if the racers back there are letting gaps go because you may be at your limit and then the guy in front of you gets gapped.