Not as many as you might think.
From The Adventures of Captain Bonneville, U.S.A., in the Rocky Mountains and the Far West..., Volume 2
By Washington Irving, Benjamin Louis Eulalie de Bonneville(pg 449)
The outfit of trapper is generally a rifle, a pound of powder and
four pounds of lead with a bullet mould, seven traps, an axe, a
hatchet, a knife and awl,a camp kettle, two blankets and where
supplies are plenty seven pounds of flour. He has generally two or
three horses to carry himself his baggage and peltries. Two trappers
commonly go together for the purposes of assistance and support a
larger party could not easily escape the eyes of the Indians.
The original story, written and published in 1837, was from Bonneville's notes and maps concerning his Expedition of 1832.
Concerning the second part of your question, From a web page concerning western history:Traders, Trappers, and Mountain Men
The fur trade actually reached its peak sometime between 1830 and
1832. At that time, pelts brought trappers an average of $4 to $6 per pound. A resourceful Mountain Man could trap 400 to 500 pounds per
year. By 1840, the price had fallen to $1 or $2 per pound, and
depletion of the beaver reduced the average trap to 150 pounds--hardly
worth the time of an ambitious man who could otherwise earn $350 to
$500 per year. By 1840, perhaps only 50 to 75 trappers remained in the
West, a far cry from the 500 to 600 who worked in the region during
the late 1820s.