Customer Onboarding Schedule across months

Hi folks

I'm trying to create a customer onboarding schedule, using an annual count as the input, and then divide the annual over 12 months.

My example of a wholesale business:
- Onboard 4 retailers in year 1, evenly distributed across each month of the year (ie: win a customer in March, June, Sept, Dec)
- Each retailer has a purchasing profile: 0 in month 1, 100 in month 2, 50 in month 3, 50 in month 4, and 10 per month ongoing

I can hard code, but would prefer an assumptions table to test revenue impact when accelerating retailer purchasing and retailer onboarding.

My question is: What's the best formula functions to pull from the assumptions table and distribute across the months, and layer on new customers (ie - by July we have 2 retailers with a cumulative product count)

Thanks in advance! I'm stumped how to schedule this out.

**edited to add attachment**

Here is a low tech proposal for getting the number of wholesale sales:
1. List the retailers in C23:C32
2. Starting with column G use the following: =IF(F$18=$C23,$E$9,IF(E$18=$C23,$F$9,IF(D$18=$C23,$G$9,IF(SUM($C23:F23)>=$E$9,$H$9,""))))
3. Populate row 19 using: =SUM(D23:D32)
For retail sales:
1. List retailers in C35:C44
2. Starting with column H use the following: =IF(F$18=$C35,$F$10,IF(E$18=$C35,$G$10,IF(D$18=$C35,$H$10,IF(SUM($C35:G35)>=$F$10,$I$10,""))))
3. Populate row 20 using: =SUM(D35:D44)
Let us know if you have any questions.