Pedestrian counting algorithm
I think what you are asking is about the feasibility of your pedestrian algorithm.  

There are two general strategies for this kind of problems: 


(bottom-to-top) Consider it as a pure detection problem, where in
each frame you detect only pedestrians. Once you detect them, a)
counting their number in a frame is fairly easy; and b) tracking any
of them in consecutive frames is also easy. Therefore, you solve everything.
(top-to-bottom) Consider it as a action recognition problem, where you detect whether a ROI in consecutive frames is a pedestrian or not according its actions. Once you solve this problem, then you solve the detection and tracking problems simultaneously.  


Your heuristic algorithm is in the first category. I donot want to discourage you, but you might miss the key point that how to detect a pedestrian. Because real data can be more complicated than what you thought. For example, if this is a subway camera, whose frames maybe full of pedestrians and thus removing background or detecting blobs does not help at all. In this case, it maybe more reasonable to use face detection and face recognition algorithms to solve the problem, because if you find a face you find a pedestrian. On the other hand, depending on your definition of a pedestrian, it maybe true that not everyone appeared in a frame should be treated as a pedestrian. In this case, it might be reasonable to use action recognition algorithms (the second category), where you can explicitly define a pedestrian based on his or her behaviors.

Here are some tips based on my experience:


Stick on what you know and what you can easily pick up. Donot invest
your time on something is fancy but requiring many backgrounds you
donot have. Trust me, all these algorithms will be good in some case
but bad in some others. Therefore, the first thing is to make
something work, no matter how good or bad it is. 
Know more about your data and then determine your method. A general description about a problem is insufficient in many cases. 
If you want to demonstrate your idea,  it is better to use MATLAB and build a prototype.