I don't want to discourage anyone from experimenting, but I thought I'd point out a couple of potential obstacles.
First, you won't be able to inflate it by mouth. Nemo beams use 6-9 psi and you'll never achieve more than 2.5 psi with your lungs. This might suffice if the beams are 4" in diameter, but then the weight becomes prohibitive. You'll need the pump.
Cuben will develop pinholes. Polyester film has a flex fatigue problem and tiny ruptures eventually occur at the creases. Large cuben kites for surfing sometimes have inflatable cuben leading edges but they use a polyurethane bladder in a cuben sleeve. This is the reason that a durable cuben inflatable sleeping pad isn't practical.
Heat sealable nylon will be at least triple the weight of the carbon or aluminum poles that it replaces. Also, in order to withstand the required pressure (particularly in the sun on hot days), the seams will need to be in shear, which will require a curved tubular jig.
The advantages of inflatable structures are only fully realized (rapid deployment, small packed size, low weight) when the structures are very large (field hangars for aircraft, large field hospital tents, etc.). In small structures you don't get much benefit from this kind of design.
I think this idea is only tenable if you use a bladder-in-sleeve beam design, higher pressure (10-15psi), and small diameter (2") commercially available seamless sleeves (polyester or nylon). You could use a presta bike valve and a mini (less than 2 ounce) bike pump.