how many gallons of water are in 200 feet of 1 1/4 pipe
1.6 gallons of water.
up to 2.300 PSI
It depends on how much each pipe can hold. And how long each pipe is.
Copper can rust
The price varies according to the diameter of the pipe and the thickness of the walls. 100 feet of type K 1/2 inch copping tubing in a coil retails for about $250. Type K is used for underground water lines. 1/4 inch is about half as much. You can use thinner type L pipe indoors and it sells for about 20% less.
Galvanized pipe will be silver/gray color. Copper will be copper. Use a magnet, it'll stick to galvanized pipe but not to copper. Drinking water lines should not be black steel pipe.
Get rid of the entire copper pipe and fit 3/4 PEX from the street main into the house. Cheap and reliable.
With a saw or pipe cutter.
It depends on the cross sectional area of the pipe.
The copper pipe is reacting with metallic elements in the ground which in turn creates oxidation in the copper, which causes corrosion, which leads to holes in the copper pipe.
Water
About sixteen feet