I have my first client... Now I need a business model! (Copywriting)

Hello r/freelance

I need some help gathering price points, and possibly even a potential business model. I'll keep this brief so I don't bore anyone with the minutiae, but I will be happy to answer any questions and I greatly appreciate any answers any of you can give me.

I'm casting off on my own as a freelance copywriter. My experience is 90% with radio advertising, so I'm sticking with that for the meantime. I met with my old boss today, and he would like to have his sales staff go and sell my services along with their advertising packages. What I need is some advice as to how to price my time, and how I can make it lucrative for the sales staff, so they will be motivated to sell.

Before I continue, I just want to make it clear that I don't think I have all the answers, any examples I give are based mainly on educated guesses. I'm attempting to gather as much advice and as many resources as I can before I start this venture. Nothing is concrete yet, so everything is on the table. What I have so far:

Commission: How much should the radio cluster keep if they are selling me? I see the pros and cons of low vs. high here, but I'm wondering if there's any sort of framer of reference here. My gut tells me it's somewhere between 10-20%, but that's only base on my past experience selling actual advertising.

Pricing: By design, there's no real standard for freelance rates out there (that I'm aware of). Is there any sort of structure based on percentages though? If someone buys a 6 month advertising plan, is it reasonable to then ask for 5%-10% more ($5,000 plan, +$250-$500 for copywriting)?

If anyone out there has any experience with anything like this, I would be glad to hear what you have to say. My goal is to eventually branch out regionally, perhaps have some people underneath me, but for now I want to find a suitable structure that's sustainable for the near future.

Thanks in advance!