Hello.
I've clearly read your requirements and it's very interesting.
I have exerience in building b2b2c shopping mall using php and laravel.
Did you comleted some payment gateway for your site? If so, you will complete order sturcuture and cart pay logic.
If you are going to add first payment gateway, then your sckript will be more complex.
Please contact me. I can complete your job. Thanks.