Try to get something like a fully managed VPS with hosting services (DNS, Email, MSSQL) etc. This will be a lot more cost effective than getting a reseller account. Beware also of hosts offering unlimited domains - for one you won't get very good server performance on these plans and for two you'll probably get asked to upgrade / move on if you actually host 200 domains on these plans!
I have seen Resellers hosting 500 - 700 domains within their reseller account. Ofcourse that depends on the resources your webhost is offering and your account actual usage.
Cluster Hosting - like Hsphere etc. support multiple server hosting, Like you have Separate server for FTP / Database / Emails and backups, in this way your all end users will be on different servers, in this way you can avoid any unpleasant episode which can happen with One Server hosting
VPS Hosting has it's own benefits like more CPU resources and control on your hosting server, which you will not be able to get in Shared server reseller hosting.
Gineey - JodoHost.com
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