I think the “minimal” setup you can go for is doing what we do with team support here, it works quite well.
You give all your clients an email they can contact you at, they then use that for all support.
Internally all the support goes to the @team group, that is one of the recipients of the emails.
That way you have absolutely no setup for new customers, no need for additional groups, stuff remains simple.
If you need a “new support request” button on the site, you can add one via a customization and link it to “auto fill” a private message.