The valves and tubing specified by FRC are specifically chosen to LIMIT flow rate... you want to maximize it.
When we built a t-shirt cannon we used a sprinkler valve
https://www.homedepot.ca/en/home/p.1...000769546.html
Note that these valves are designed for water pressure, not air pressure. A small crack with water pressure causes a small leak. A small crack with air pressure (compressible fluid) causes an explosion.
The same thing applies to your compressed air storage tanks. Don't assume that a 200psi rating on plastic pipe makes it safe for holding 100psi of air pressure. You will likely be using some components outside their designed applications... it can be made to work (you'll see lots of people doing it on online videos and instructables), but we chose to use air-pressure rated pipe black iron pipe as our storage tank. Maybe a bit conservative... but just be aware that the same energy that goes into launching the shirt can also go into launching shrapnel if your tank or valve lets go.
Another feature to consider adding would be an IR or ultrasonic rangefinder on the tip of your cannon barrel that disables firing if an object is detected in front of the cannon barrel.
I assure you, the results will be pleasing. We had to dial back the pressure on ours because we were bouncing the shirts off the gym ceiling, rather than arcing them nicely into the stands.
Jason