Question: At the beginning of the move it is established that Big Jake has not seen his sons for 10 years, but it appears he is close enough geographically to be found, summoned and arrive before the bad guys can get more than a days' ride away from the ranch. Was he really that bad of a dad or is his arrival at the ranch a bit too magical?
Answer: He has been gone for 10 years but knows "Juan and the little boy", not 10 years old I assume.
Answer: Jake was a very rough character when he was a younger man, and his wife did not want him around. After the grandson is rescued, the family realises he has changed and they reunite.
Question: At the beginning of the movie I counted 9 bad guys. We only see 1 die, then there are 6 - what happen to the others?
Answer: According to Wikipedia, the shootout at the ranch, both Devries brothers are killed by Jeff McCandles, before being shot himself. The rest die at the end of the movie.
Question: What is the weight of the million dollars in $20 bills?
Answer: A U.S. bill weighs roughly 1 gram so that about 454 bills (regardless of denomination) weighs 1 pound. It takes 50,000 $20 bills to equal $1M. Which is about 110 pounds. Of course this is freshly minted weight, so any debris and anything used to secure the bills would increase that weight).
Answer: It doesn't help explain locating Big Jake or time involved, but as to helping some with the quickness of him coming to help, remember he came in on a train, he didn't ride back home.