There are many cow herds with Angus cows that are excellent mothers, some too good that the producer can't get near the calf without having momma blowing snot down his back pockets. Some Angus herds, though, may have cows with not so good mothering ability. It all depends on the individual herd and what producers have selected into or out of their Angus cow herds.
Angus cows are beef cows, not dairy cows. Holsteins are dairy cows, not beef cows, which is where we get the majority of our milk from.
A popular choice for breeding with Angus cows is a Charolais bull. Charolais bulls are known for producing calves with good growth rates and carcass quality, which complements the Angus breed well. Other suitable breeds for crossbreeding with Angus cows include Hereford and Simmental.
Scotland.
Angus cows or heifers come into heat every 21 days.
No.
Brahmans are known for their great mothering ability, yes.
No. Black Angus cows are all black. You can only get black cows with white faces if they have a sire as a Hereford or traditional Simmental. These cows are called "black baldies" and should never considered as purebred Angus because they are not purebred at all: they are crossbreds.
Scotland.
Semen that is ejaculated into cows to produce Angus-sired calves.
meat, hence "angus beef burgers"
The things that are made from Angus cattle are exactly the same as what would be made from any other cattle of any other breed: hide for leather; hair for upholstery, paint brushes; the list goes on.
Aberdeen Angus burgers are made from beef which come from cows.