I think the build-up versus straight porn might vary depending on fandom, or on the individual author. Me, I like a lot of plot with my sex, so I look for build-up, and an actual storyline when I’m reading. Even when I’m writing, I prefer there to be a plot, and some build-up to any sex.
From the perspective as a woman, she won’t necessarily get tired after the first orgasm, but the next orgasms will cause increasing sensitivity and eventually literal discomfort can occur. So, if she is having sex with multiple partners at the same time, she might not have an orgasm with each partner, or she may very well reach the point of snarling at the hapless partner who triggers that discomfort threshold. Realistically speaking, that is...