I'm struggling a bit to understand what you are trying to accomplish.
I've got a Foundry VTT license, so I can help. But I'm not sure what you are asking from us.
Do you just want us to setup a Foundry VTT instance? Or, are you expecting us to then play games with that instance?
Are you just trying to see how many instances of Foundry VTT can be installed on a host, or are you trying to determine how many simultaneous games can be run on a host without impacting performance?
The way Foundry VTT is designed is as a "thick client"; most of the code is javascript running in the player's browser. Only a small part, the shared database and a little synchronization and data cleansing code, is running on the server. So a relatively low-powered server can run several Foundry VTT instances simultaneously. And the number of clients should not appreciably increase the workload on the server; the work is distributed and is performed mostly locally on the player's browsers.
In the case of running Foundry VTT locally, you are generally using an Electron wrapper, and are running both the Foundry VTT server and client on the same system. That definitely eats up CPU (my laptop fan starts really getting loud). But most of that load is from the client and Electron, not the server.
In addition, the load on the server is affected by whether you are using it as an A/V Relay server as well. Foundry VTT supports WebRTC, and using that can affect performance, and subsequently the number of concurrent instances of Foundry VTT that can be run on a server.
So, it is important to understand what the scope of the experiment is.
1. Do you want us to just setup an instance? Don't need to run a game, just setup the instance.
2. Do you want us to use this to run games? (If it is only available until end of May, these will have to be one-shots; I wouldn't want to switch to it temporarily for my campaign, it's too much work.)
3. Do you want people to run games concurrently? Then we need to setup people and times to run the games. And players will need to understand an experiment is underway, and performance may become poor during the game.
4. Do you want to have A/V integration enabled in Foundry VTT, or simply use Discord for A/V?
5. What is the performance criteria? Max CPU utilization? Performance lag in sending updates to clients?
Setting up an instance to actually run a game can be a lot of work. You've got to upload characters, scenes, items, and journal entries, as well as various assets such as pictures, battlemaps, and audio. And you have to realize this system is going to go away in a few months.
Another direction to consider is to contact Atropos (the developer for Foundry VTT) and ask him if he happens to have a test harness available that would stress your system and multiple instances. He might even be willing to provide you with test Foundry VTT licenses for temporary use. Couldn't hurt, and might save you a bunch of headache.