i use a nikon, but im sure it translates to canon anyway.
i had a 50 1.8...then i got my 24-70 and never used the 1.8 again.
i sold it as i now dont need it. low light capability will be excellent with 5d anyway with the 24-70.
poss best to see how you get on with the 50mm as its cheaper
but i think 24-70 is a great range for studio work