First and foremost - food. I'm assuming the aliens can provide enough water, interim food, and electricity, but that the humans will eventually need to grow their own food.
Assuming the Collectors are intelligent enough to abduct some farming equipment and some seed stock, humans can easily support themselves by farming 2 acres of land each, with four growing seasons (made easier if this is an artifcial environment with no cold season). This figure decreases if community farming is set up, but for this purpose I'll assume you need an even 150 acres of land to allow for breeding/population expansion.
Second, living quarters. If we take the prison requirements from <PERSON>'s answer, and add a little extra, we can have 9 blocks of 8 single occupancy cells. Each cell measuring 8m². Each block of cells enclosing a sanitary facility measuring 12m², with four 4mx2m cubicles on opposite walls (shower and toilet cubicles are the same thing. 548
Waste goes down the same hole!) So each block of cells measures a total space of ~30m² when wall space and corridors are accounted for. Residents will need a communal area for eating/socialising. Lets add another 30m² room to the centre of the 9- block complex, bringing the total living space requirements for your colony to ~300m². This is not even taking into account the idea of multiple floors, so this part is really down to what you decide the Collectors will build for the humans.
Human are also going to need something to do. Not everyone will be working the land at once in a community setting. Various recreational activities will take up space. Sports courts, running tracks and swimming pools, as I assume the Collectors will want to show off our greatest assets (these aliens can move quickly on land AND in water?!) will likely take up most of your space requirements.
This can't all be bunched together either, you need paths, roads(?), open areas like parks(?) if your Collectors are nice.
In total, my estimate for a functioning human safari park with farmland, accommodation, and that shows off the best traits of human evolution, you would need around 1000m² of space. 87