I can do a few normal push-ups, just nowhere near enough or fast enough to keep up within the circuits. Its one of the things I really want to work on in my next round.
I was ok with the walkout pushups in level 2, as the walking out and back bit gives you time to recover between each push, iyswim.
I think the first plank in circuit 1, level 3, is tough to begin with, but you do get stronger with it quite quickly. I struggled a bit with it at first, but its fine now. I think the key is to keep your plank low and make sure you are using your abs and keeping your weight over your arms, rather than letting them get out in front of you.
Rock star jumps are killer. It took me a while to get them right. I found it helped to think of it as a jump first, then a kick upwards a second afterwards, as when I first tried it I couldn't seem to get my heels up high enough.
I thought I was ok at the jumping lunges the first time I did them, but then found my legs just didn't want to do any on the second set of reps.
I can manage 10 jumping ones in each set of reps before I have to give in and do Anita's static lunges instead.
The plank rows with a leg lift that you mention are fine for me in terms of the move, but I find my hands hurt holding my dumbells and I actually have carpet burn on my knuckles from it! [shock) I'm doing Natalie for the first set of reps and Anita for the second, but being careful to keep a solid plank and tight abs, even though I'm on my knees for the second lot.
I am still doing Anita for the hip raise things at the end (I don't know what they're called either). I find I can do them fine when launching off my left hip, but not so good on the right and wonder if that's because its my right leg (so my stronger side) that helping when I'm lying on my left?
I know what you mean about feeling disappointed. I was the same when I first started level 3, then it seemed to get easier/better and now I feel like I've slipped again and need to up my game. I'm determined not to miss a day this week, as I do think all the enforced days off last week had a negative effect.
Measured myself today though, to try and stay motivated and have lost another half and inch here and there, so at least I know something is still working. 
I've definitely decided to buy Banish Fat Boost Metabolism as well now. I feel like I need to improve my general fitness/stamina as well as doing the circuits and I reckon in order to do that I need to get in some extra cardio sessions.