Do a lot of research and reading on VPS Service, particularly X10 VPS service.
VPS is not for everybody. VPS service at X10 is bargain priced and is offered by a great company, but it is UNMANAGED service and X10 does not provide any support for VPS unless something breaks on their end, which is very, very rare.Therefore you will need a very good working knowledge of Linux, Apache, MySql, Perl, DNS, Mail Servers, and Shell Commands, just to name a few things.
Also consider that while X10 can provide you all the disc space and memory you need, your choice of operating system and how YOU configure and manage the server will have a large impact on the performance of your server, domains, and websites. Again, this is something that comes knowledge and experience. If you feel that you have adequate knowledge and experience, as well as the time and patience to maintain your own server, then go for it. But, as Daniel stated, the best choice for the majority of people is a good paid hosting plan from a good company - like X10.