Plentee; double; lap over; ends; crack

Hi,

He loved to play Chinese lottery. Also, in his gambling, he had one besetting weakness—faith in a system; and this made his damnation certain.
For to play a system requires money, while the wages of a gardener's helper do not lap over the needs of a wife and numerous progeny.

1. What does "lap over" mean?

2. What does "play a system" mean?

"You might wrap up the goods before you deliver 'm," the stranger said gruffly, and Manuel doubled a piece of stout rope around Buck's neck under the collar.

"Twist it, an' you'll choke 'm plentee," said Manuel, and the stranger grunted a ready affirmative.

1. What does "doubled a piece of stout rope" mean?
2. What does "Twist it, an' you'll choke'm plentee" mean?
3. Does "grunted a ready affirmative" mean "grunted to express agreement"?



But when the ends of the rope were placed in the stranger's hands, he growled menacingly.

1. Do "ends" mean "both ends"? It doesn't quite make sense to me.

The hoarse shriek of a locomotive whistling a crossing told him where he was.

1. What does "whistling a crossing" mean?

"I'm takin' 'm up for the boss to 'Frisco. A crack dog-doctor there thinks that he can cure 'm."

1. What does a "crack dog-doctor" mean?

The kidnapper undid the bloody wrappings and looked at his lacerated hand. "If I don't get the hydrophoby—"

"It'll be because you was born to hang," laughed the saloon-keeper. "Here, lend me a hand before you pull your freight," he added.

1. What does "hang" here mean?
2. What does "pull your freight" mean?

But he was thrown down and choked repeatedly, till they succeeded in filing the heavy brass collar from off his neck.

1. What does "filing the heavy brass collar from off his neck' mean? They removed the collar?

Thanks in advance