1. backfill is not a problem, also "pressure bar" doesn't work.
2. my english is bad, but if I understand what you say the first line doesn't change, but probably I haven't understood.
3. no, I think otherwise; yes we can use only the bid/ask volume, but using the total volume we have more informations, we can weigh better the streght of up/down trend. Image to use only bid/ask volume, we could have CMF = 1 (or -1) also if there are few volume to ask (or to bid) and many to bid (to ask), but with total volume in the denomiator you would have a CMF << 1 (>> -1). With total volume in the denominator when CMF >> 0 (<< 0 ) (+/- 1 are very unlikely) say that price and volume are going in the same direction.
How I have written, is only a my idea.