Ask HN: 409a from lawyer or informal email to cover early equity split?

I founded a company about a year ago and will do $80k on sales this month and $100k next month. I hired a marketing consultant in April who has done an amazing job and really helped get us to where we are.

I pay him and I am still a volunteer.

He is asking to be made co-founder and get 30% equity.

I have no idea what to do but an acquaintance who is a VC said I should first get a 409a from a lawyer to determine the value of the company then back into an equity split.

Is that premature? Should I just email something like you get X% and co-founder title vesting over four years with a one year cliff?

Bonus question is how much equity do you think he should get?