Well, it seems nobody answers to you, I´ll do.
I´m also calculating for reseller plan. Two of the main things I found are important: space and bandwith.
Some free hostings gives 15 to 25 mb space and 500-1Gb bandwith. Ok
Paid hostings do from 25-50-100 mb space. Bandwith between 1Gb-5Gb. Depends on the price and service you are giving. For example: Netfirms basic plan costs $60 a year with 50mb space and 2g transfer, but no mysql. Sometimes space is not important, is the bandwith, depending on what people wants to upload. If you give too much space some will upload large files and large forum databases.
Control panel is more attractive. Use CPanel 4.9 or Plesk.
PERL-CGI, PHP, Mysql and POP e-mail should be basic in your plans. Not necessary unlimited. Ha!, don´t go for unlimited space and bandwith, is not reliable.