The more knowledge about the software running on your server and programming languages, the better off you are. If you become a reseller, all server issues you get from your customers will have to be forwarded to your host, as you have no control of the server's behaviors. You can always say you won't support the various programming languages on your server and tell your customers to find a place which is dedicated to supporting those languages, but it would surely be nice to be able to answer any questions of their's.
If you buy a reseller pakage - you do not have to wory about tech. The only thing you need - to know how to use your browser to access your Admin Panel. And it's easy to manage your client's accounts as having Cola at any MacDuk.
Another thing - is to get a good deal.