If there are no hills, do not bother with gears.
Students who can use a free bike will be happy enough with a bike that actually works and does not break down just when they need it.
If you look at the most popular rental bikes in the Netherlands you do not see any gears.
(But if you think it is needed, three gears (or up to 8 gears) inner hub gears work well.)
I have recently been cycling in the dunes quite a bit and see a lot of these (no gears) rental bikes. While the dunes are not high, the roads through them tend to go up and down all the time.
Young adults are less likely to want gears for a relatively flat area than any other age group. And students who can get a free or very cheap bike with no gears are more likely to take them, especially if the alternative is more expensive.