No, there’s no maximum number. Channels are pretty lightweight, they’re not explicitly created or destroyed.
I haven’t worked on that area of SG in a while, so my knowledge of channel handling is probably out of date, but from what I remember the overhead is more about the total number of doc-to-channel assignments (i.e. assigning every doc to hundreds of channels would get expensive), and about the number of channels that a user has access to and pulls from.