Just a couple of thoughts...
1 - The amount of air needed depends on the pressure setting you choose on the cutter (based on metal thickness, etc) and how hard / often you're using it (duty cycle).
2 - You can use the smaller compressor & add a portable tank in line with it. That'll give you a bigger buffer of air for longer sessions, without necessarily having to buy a compressor. Increasing the regulator pressure will further increase the buffer. The higher the pressure is coming into the cutter, the lower the flow through the system.
I'll also put in a second for the Lotos mentioned earlier. My wife bought me one a few years ago and it's been good. I'm a farm boy and have cut metal a lot of ways. That's been the easiest I've used. It's small, but does the job well. Cuts are clean and parts are available on Amazon for replacement tips, etc. I used it a few weeks ago to cut holes through a 1" plate upright on an old implement. It took some maneuvering, but I was impressed. That's way thicker than what it's supposed to do. It did need a new tip afterwards, but I'm fine with that.
There's still some deburring to do, but not bad. Better than a torch and the burrs aren't sharp like with a cut-off wheel / grinder.
Hope that helps.
