You would need a billing system, you can also look at iPanel since it's targeted towards free hosts. I'd recommend WHMCS over all though.
Any provider that gives you unlimited bandwidth on a reseller account is probably not reliable. Plus the fact that a lot of hosts don't allow free hosting due to the major issues with abuse. You might want to look at getting your own server, and at the very least manually screen your orders and use something like MaxMind.
I will also say that the free hosting business is incredibly hard to make any money at. 95% of free hosts disappear within about a year.
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XPanel is another great choice for an automated free hosting control panel. However, with XPanel, you'd have to be willing to upgrade to a VPS or dedicated server. XPanel requires httpd.conf modifications and file placement in the /usr/local directory.