Hi there,
Thanks for your question.
What i believe sending the plan text format to the email always risky or security breach for customer. Upmind does not store any passwords and when customer requested new password it will directly connect the cPanel API and generate password. So suggest you always encourage change password through upmind dashboard portal.
cPanel URL depends on your hostname configurations by defaults it will be your main server host name. cPanel.clientsdomain.com will be take as feature request.
Thanks