Rule Of Thumb For Customer Service Modeling

Hi all,

I'm trying to put together a financial model for our ecommerce brand as we are well positioned to seek investment and take a huge step forward.

So far, I've been doing all the customer service myself.

If/when we take the next giant leap, we will need to hire customer service staff to keep up.

My question is this:

What is a good rule of thumb for customer service staff required vs daily sales?

I know this can be very fluid, but if anyone can shed some light from their own experience that would help a lot.

Thank you.