Greetings!
Please see my proposal below:
We will install and test everything internally on my local server (or yours if you prefer).
I'd use a Google Compute Engine VM, Debian 9, Asterisk 13 latest stable.(By default it ships MariaDB). You may also tell me specific versioning requirements.
Are you open to alternatives to asterisk realtime, instead use scripts to generate static config files/folders from mysql db, that can be included?
Digium's fax module is withdrawn now for the versions proposed, so we could opt for res_fax_spandsp module or iaxmodem/hylafax. Fax success over VoIP is sensitive to many factors, as you may be well aware, all of which we will discuss.
For multi-tenanted billing we can use the adaptive cdrs for each tenant.
Though it may not be so apparent from my current profile, I am an experienced and successful asterisk consultant and can provide you references on request. I consider the bid amount low but I am eager to get started to some freelancing work.
I am based in Chennai, India and can be available generally until noon Eastern time.
Thanks - Maha