Do you sell? or your co-founder(s)?
The answers should be: (a) more than 5; (b) Yes; if No, then should be (c) Yes.
I am not being snarky. It has been shown time and time again, that when you are starting out, at least one of the founders should be selling. Hiring an experienced sales managers will not result in sales, they are "managers" so they will hire more sales people and thus increase your burn rate.
Ok, I guess you don't believe me. So why don't you let Google be your friend and find a few articles along the lines of "Things I wish I knew as a startup founder".
So you need one salesperson, not a manager. Not knowing how much profit each customer generates, you need to do your numbers. A good rule of thumb is that a salesperson needs to generate 3-4x profit / customer for their commission and their anticipated annual commission would need to be at least 2x what they could earn in a "typical" job for that age, knowledge and experience.
Especially with enterprise customers - ultimately, each can be as productive a pipeline, even moreso long-term, than an individual salesperson.