Re: Spaying/neutering ferals
Males recover quicker and have less problems than female cats, though problems can arise. Statistically, it is lower for neutering vs spaying since spaying is so 'invasive' into the body cavity.
If your cage is large enough to have room for a bed, litterbox, food and water ... yes, I think it would be fine, especially if you could keep it out of full sun. If you could provide shade for a sunny spot AND a fan to blow air into the confinement area, that would be the very best you could do for these cats. You are correct, they *do* live outdoors in these extreme conditions year round so they are used to it. The only issue is that surgery, anesthesia and stress can make them susceptible ... so the more stressors you can remove, the easier their recovery will be.
If you could make the confinement cage large enough to hold enough food/water and litter for several days so you didn't have to go *into* the cage daily to clean and add food/water, that would help lower the stress of confinement. Try also to keep the confinement area in a relatively 'quiet' place, meaning not a lot of people coming near the cage.