Why 了 can't go after 酒?
Most often goes after the verb.
It usually goes immediately after the verb
It can as the second 了, it'd sound unnatural as the only one and after 酒
Nice they count beer in glasses, not bottles or barrels :D
Traditionally it was really tiny cups like teacups with the teapot.
Is the 'le' really needed after 'he'? What happens if we left it out?
The 了makes it past tense. Without it it's ambiguous; you might be asking how many she intends to drink.