Licensing question

[Clayton Dukes]

Hello License Gods :-)
I'm trying to figure out which licensing best suits my goals:

1. I want to allow smaller companies, say less than 50 employees, use
my software free of charge.
2. Larger companies will pay a licensing fee (based on the size of the company).
3. Any modifications/bug fixes should be shared back.
4. Users cannot use my code in a commercial product without my permission.

Can you recommend a license that fits this ideology?

Also note (not sure if it's important?)
My software is written using other open source programs, such as PHP -
does this affect my license?

Thanks!

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Clayton Dukes
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