Selling the "application" single end product

I’m a self-entrepreneur and quite confused!
I would like to buy a CRM on Envato, host it on my server and charge a monthly subscription to my customers to use it (1 CRM installed per customer) with updates, maintenance, development of custom features, etc. .
I don’t know which license I should use for this?
Do I need to take a Regular license per customer? An Extended license for each customer ? One Extended license for all customers?
Knowing that I can modify the design of the CRM, can this be considered as ONE end product?
Thank you in advance for your answers!