There's no limit, but there is probably a limit to where she can be satisfied. I remember Phoenix Marie saying in an interview that she'd love to fuck four men at the same time, but she can't handle becoming a "cum tray".
Two hands - two guys
Two feet - two guys
Pussy - one guy
Asshole - one guy
Mouth - one guy
I guess that makes 7, without having to have guys wait around? Unless SpexyAshleigh is right and the ear holes and nose holes work for sexual pleasure.