I'll try my best to answer this but first just want to point out that 72 people is not enough for coming from every background, race and ethnicity, it would be enough to represent every language, culture etc. to give you an example of this, would anyone here care to say that a New Yorker is the Same as Texan? anyone? because they are both American, and therefore much more similar than say an American to a Greek. hell an American is closer to a Canadian than a Greek, and yet if i suggested they were i'm pretty sure it would anger a lot of people. because although both american they're mannerisms are different.
it would make more sense from a cultural perspective to have a subset or breed of humans the same as we have with penguins etc. South-African, Rock-Hopper, Emperor, King etc. they are all penguins but they either look or act different enough to be a different breed. same with pigeons, dogs, etc. so you'd probably have the New York exhibit, the Texan exhibit and the Greek exhibit, and so on, with a set of human abductees in each, both male and female, and enough that a breeding program could be setup to maintain the Zoo's numbers.
it moves nicely into my next point... cultural differences. anyone who lives and is happy in a city, is generally happier living in a smaller space than those from the country, but oddly, they often prefer that space to be more private, than those in the country who tend to while maybe not prefer but will except less private personal space (rampant generalization there but in my experience it tends to hold true)
Now that's out of the way...
but as a rule, most people on earth will happily get by with a couple of square metre bedroom, nothing more, so long as its got enough space for a bed, they're happy. its functional not a hangout space. now i'm sure most people here will disagree but think about it, most of the planet live in China, India etc. Western culture populations which tends to treat a bedroom as a place to stay in rather than just sleep, is very small compared to the population of the rest of the world. US is 300 mil, uk only 70 mil, china over 1 billion!
This is where the "breeds" of humans would come into it to rectify this issue
again i digress, so a few square metres bedroom, enough for a bedroom, set of drawers, maybe a bedside table... standard single bed is 1 metre, by 2 metres roughly so probably about 4-6 square metres bed across the back, 2 metres by 2 or three is plentiful (for most of earth at least), each, so for your numbers 76 rooms with at 4 square metres absolute minimum each.
For food and socializing, a 12m x 6m (40ft x 20ft) Marquee will have room for 8 tables of 10 guests, 80 in total, make it a little bit bigger to make socializing better, if all these useless humans do is sit around and eat then the alien public aren't going to pay to see that again and again. which makes the exhibit not worth doing. so call is 12m by 10m,
Wash and Toilet Facilities...
1m x 1m for each stall is about average, so enough for a staggered use for showers, you'd want about 8 showers, and about 8 toilets, plus basins etc, so about 6m x 10m would be more than enough, and remember when people go to the zoo often its the small habits like cleaning and eating that people go "look its doing something."
So put all that together and for the numbers you've given and for a fairly bland and uninteresting Zoo. you'd have roughly 484 square metres give or take areas where the aliens would install walkways through the exhibits to get a closer look at the animals as is common with zoos and aquariums here on earth.
of course if you started adding farmland so "here you can see the how these primative creatures gather food" and a gym "so you see here how the males do there best to impress the very unimpressed females", or even a figh... a club i'm not allowed to talk about... to show off the combat skills.
Edit: Mental Health
This is another thing that changes drastically from culture to culture, but often socializing is a more sure fire way to improve/maintain good mental health and environmental factors, this is often more important when it comes to members of the opposite sex. Prisons are an example of if you place people who all tend to be annoyed in some way in close quarters that these general rules don't apply, prisoners often need more space than "free" people because without room to distance themselves when needed, there tends to be riots.