I’ll try to answer your questions.
How many laptops can a raspberry pi can realistically support?
Traditionally this has been between 10-15 but it’s hard to say without testing first. Using the latest model of the pi will help with user count. Connecting the pi to a wifi router to provide the Wifi while the pi is used only to provide RACHEL will greatly increase that count but can be more complicated to connect to and set up. If you’re looking to have more than 15 users connected in one classroom I would suggest looking at the RACHEL-Plus devices which can support many more users at once as it’s much more powerful rather than using multiple Pi devices. Two people I know have deployed the RACHEL-Pi recently are @giakonda and @SHOMI. Maybe they can help with their experiences with device counts.
Is there a way to set a limit to only have certain laptops join certain pis?
This is something I would like to make easier in the future. The easiest way to do this right now is to secure the wifi hotspot with a login and password that only certain users or laptops know and designate those laptops to use that hotspot. I’m not sure how familiar you are with this but I can help you with it if you’re interested. It requires changes to /etc/hostapd/hostapd.conf file on the pi.
In the event that one Pi shuts down how do we transfer those laptops connected to a new Rachel Pi server?
The Wifi Hotspot the RACHEL-Pi creates is open for anyone to connect to and access content. If one Pi shuts down they will be able to connect to another. If you add a login and password to the pis, they will need that login and password to connect to the new device/hotspot.
If you plan to use Kolibri, it can be set up as an open facility without the need to log in to access content but if learners use Kolibri to create their own user accounts and track learning, their profiles and progress will only be on the device they created their accounts with. If it shuts down they won’t be able to access their profiles on the new device they connect to. If they connect to another pi they will have access to the content on the new pi but they would have to create new Kolibri users to track progress. The Raspberry Pi can use either a Micro SD or USB device for storage. All of the content including RACHEL is contained on the storage device and can be used in another Raspberry Pi if one breaks.
Would we need a router if we have multiple raspberry pis in one school?
The Raspberry Pi devices act as individual devices that are separate from each other. You won’t need a router to have multiple running. To avoid conflicts between the wireless signals and make it easier to connect to you would need to change the Wifi SSID and channel in the /etc/hostapd/hostapd.conf file. This changes the name so you would have RACHEL-PI-01, RACHEL-Pi-02, etc.
I can help you with any of these changes if you decide to use multiple RACHEL-Pis. I would consider contacting someone from the RACHEL team to see if the RACHEL-Plus is more suited for your situation.
Hope that helps!