Create custom wordpress plugin

I am seeking a developer well-versed in developing wordpress plugins to develop or customize an open source membership-job management plugin (similar to how up_work manages jobs). The plugin chosen should allow me to use it without infringing copyright. The customization should lead to: 1. Job positing >Allow a user (client) to register, fill their profile and post a job offer (by choosing one category from a list that admin will provide). Clients can only post jobs in a specific ZIP code. We'll need to add a list of ZIP codes for clients to choose from in the backend. > User will be able to buy credits to post a job (payment through pay_pal). No posting job with no credit on file. Credits are purchased in blocks of $10, 20, etc > One job posting will be $10 by default > Upon job being posted, it will be available to freelancers who register and choose that category alone. > Freelancers (who will only see job description, location, and first name of poster) will respond to the job with a proposal. >Job poster will be able to see all proposals. However they will only be able to open 3 proposals to exhaust their $10 used to post it (it takes $3 to open a proposal). If they want to open more they need to deposit more money. 2. Freelancers > Allow a user to register as a freelancer, fill their profile including a biography and chooses categories (from the same list that admin will provide for clients) > Will be notified (via e-mail) anytime a job is posted in the categories and ZIP code they choose (ZIP codes from a list we provide in the backend) > Freelancers will respond to jobs by paying to send a proposal. Each proposal will be $10. They should be able to make an offer (amount they want to charge) > Whenever a client opens the proposal, then the freelancer will expend their $10, otherwise, if job is filled by another freelancer and client never opened the freelancer's proposal, then he gets a credit of $10. I will give more details and discus further with the right candidate.