Hello,
i have understood your project and i would be glad if i could get the job.
I know WHMCS very well, i am the CTO of a german webhosting company which is using WHMCS itself.
I have developed following modules (to name only a few..):
[login to view URL]
[login to view URL] <- domain registrar module
[login to view URL] <- payment registrar
On Freelancer:
https://www.freelancer.com/jobs/PHP-Linux/WHMCS-Plugin-for-proxy-service/
https://www.freelancer.com/jobs/php/WHMCS-OVH-Reverse-DNS/
https://www.freelancer.com/projects/php/Add-new-features-WHMCS-Affiliate/
Through my experience you will receive a well documented and secure module which will work stable.
I will do the development in my own dev installation and after finishing, you receive the modul which works as plug & play.
Are you using the six template? If so, then i can avoid template changes in the tpl files and everything will be done in hooks and in the module. You can also test all functions in my dev whmcs installation.
You can see here my reviews: https://www.freelancer.com/u/ebmedias.html (55 reviews, 5 stars profile)
As i am from austria/germany, i cant make the same price as the indies on this page. I think you know that you cant compare the quality of work of an indie developer vs a company from germany :)
Please let me know if you have questions.
Regards!