Neither bid sounds anywhere close to adequate.
A rule of thumb I've used is that one AP radio will support up to about 25 clients for normal traffic. If you want to support high-bandwidth applications such as streaming video, that number only drops. Dual vs Single radios don't matter much to me: it's just that if you have single radio APs you're placing more APs in the same size space, which means more switching and power infrastructure... but they also mean the APs will overlap, so if one goes down from loss of power there is likely still some service in the area.
The big thing is that even the dual-radio APs need those radios use the proper channels. With only three non-overlapping channels in the US, and only about 25 clients per radio/channel in a given space, supporting more than 75 devices in a single area — such as a lecture hall with more than 75 seats — is a real challenge.
Now the good news is that not all of your 5000 students will be online at the same time, but even assuming only 1000 concurrent users, with 25 users per radio you are looking at a 40 radios as a starting point. Remember: this is just the starting point. There are lots of factors that mean you will need more than this. Let's look at a few of these:
If you are a residential campus, you need to double this number, as it means your student body is almost entirely in one area of campus during the day (classrooms, activity areas, administrative areas, etc), and almost entirely in another area of campus (residence halls) late evenings and early mornings. Also, this assumes a perfect distribution of users across these areas of campus. That might be true in residence halls, where students have an assigned spacing in rooms that is fairly consistent, but you'll find you need to about double your initial radio count again for the more public areas of campus as students spread out and move around in groups from place to place. The residence halls have their own problems, as the concurrent user count can approach your actual student FTE at certain times of day in the halls... in other words, add that radio count again. This brings us up to 160 radios so far.
Finally, you need to look at your really dense spaces. Here, I'm talking about lecture halls, common spaces where students like to bring laptops, and stadium areas if you want to provide wifi there. These spaces will all need additional radios. You also need to look at your really sparse spaces, like parking lots and green spaces. You may not want to provide wifi to parking lots, but I'm betting there are some nice public outdoor spaces where students would like to be able to sit on the grass with a laptop. Count some radios for here, as well.
If you have older building with brick or block construction, this can add significantly to your required radio count as well, as wireless signal will lose a lot of strength passing through that material.
I know these are all back-of-the-napkin kind of numbers, but I'll be very surprised if your deployment doesn't end up at least twice or even three times what you're looking at, right down to a second load-balanced or fail-over controller.
