Hi Boris - that's an enormous amount. So many factors about your business will determine my response, but unless you really want this person to be everything, don't expect to take on many other people, then MAYBE 20. But start thinking below 10%. Of course, that's an answer outside of knowing anything about your business.
Remember, most CMOs last 2 years.
Also remember about dilution. You keep 50% now, you do a couple of rounds, you miss a number, you do a round, you aren't left with much at all.