Hi:
Good job tackling this important exercise. There are many entrepreneurs who shy away from it.
That said, if you're in the US, check out SCORE (https://www.score.org/). The organization has chapters around the country or you can connect virtually. This is the perfect type of project for their counselors.
If you wish to discuss, send me a PM through Clarity for 15 free minutes.
Cheers,
Kerby

I like Kerby's answer. I'd also suggest working with a fractional CFO service like B2B CFO. Someone with them who is experienced in building models like this will have a good template to start from should be able to put together one for your business in 5 - 8 hours on an hourly basis. If they are quoting more than that, find another fractional resource.

My firm, Venturity, can also do this for you. We're an outsourced accounting firm with higher level resources that can tackle these sort of tasks quickly and effectively. We do this for a lot of our clients already, and because we're accountants, we truly understand projecting all three statements, not just the income statement. Happy to discuss at no charge, just reach out to me with a follow up.