Hi Assaf!
I'm WHMCS admin user/developer already since v2.2 (somewhere in year 2006), did many smarty template customization, hacks & hooks, provisioning modules and payment gateways (last was The Ethereum payment gateway for WHMCS 7.5.2).
I would love to brainstorm any change on WHMCS with you.
Please note: My bid is not final - Upon discussing the details, I will update my offer and give you a new time & cost estimate.
Looking forward working with you, Professionally!
Mathew