I agree that you want plenty of exercises for the leg but several sets of leg extensions seems a bit extreme. I also see how your saying about maintaining a high HR and in respect to that id either do supersets or just sets of three with minimal recovery.

Thats just my opinion anyway, i was trying to say that as a beginner such a complex weight routine may not be as advantageous, especially once the body has made neuromuscular adaptions and further gains are through muscluar adaptions. Also theres the over looked issue of overtraining, however there are no black and white answers with fitness and exercise so i am by no means saying im right and your wrong

And good luck Stu!