I would avoid using a regular shared plan to host your clients but go with a Reseller plan with a reputable company if you wanted to host your clients.

If you go with a reseller plan each client will have their own control panel (whether or not you give them access to it is up to you) and should you need to move one of the sites to another provider or a client would want to do it then it would not be difficult.

If you host it all on one shared account (generally against the terms of service anyways) then all accounts will be linked and it would be much more work and more difficult to separate one of the sites out to be moved if it needed to be done.

Also if you get a reseller plan and give them access to the control panel they can create and delete their own email addresses etc... where as if you do it all on your own account you will have to manage everything from top to bottom.

If you do not want to provide hosting support there are a few companies out there that also provide end-user support but I have no experience with any of them so I cannot really point you to any certain one. In the end if you did not want to provide direct support for your clients HOSTING needs and could not find a hosting company that provides end user support that you felt you could trust it might just be better to place your clients with other hosting companies. If you do this, make sure to use their affiliate systems so that you get a little extra money from the deal for free

I do wish you the best of luck in your endeavors.