What is the maximum number of experiments I can have running at any given time?

There is no limit to how many experiments you can run at any given time. However, it's a good idea to keep your experiments laser focused, so you can fully understand the lift of one experiment versus another.

For multivariate experiments - there's no limit to how many variations you can have, but whittling down your experiment hypothesis to a select few is the key to understanding what is most effective.