Who cares if he will never reach that amount of players. I feel like you're all dodging his question because you don't know, feel like you should know, are annoyed about that, and want to post something anyway.
The hardware requirements to host for 1000 people will vary depending on the type of server, the scripts its running, the size of map etc.
Having never hosted for that many people before I can only offer a rough guess, which would be that your current specs will be sufficient. There are people lurking around who will be able to answer your question with experience backing it, but I don't feel comfortable tagging them in.