I would build the craft CMS plug in and it would expose a web hook to be called externally to create a new member user on the craft website. As you mention the web hook will receive e-mail, predefined password, name , company, address details.
The plug in will you would test as describe like check if the user already exists based on email, and if not it will add the new user. The response of the action will return true if the user is added and false if not.
Cost = £200 I should get in my hand.
Time = 5-7 Days
Tracy ....