There's no hard and fast benchmarks for EPiServer as it depends on a number of factors, i.e. the number of concurrent requests and sessions that you're likely to have to support and the functionality that your pages will deliver.  

With EPiServer installs I would always recommend a lot of RAM as you can leverage the caching functionality to minimise the database hits and maximise performance.

EPiServer is an ASP.NET web application that uses SQL Server, so there's a lot of information and guidance out there regarding load and performance for the platform in general.

Ultimately, the only way to be sure is to perform a proper load test to check that your planned rig will support your system and users. Given that your user base is only 1000 people I would start with a single server [with lots of RAM, ofc] and build from there.

Oh, and bear in mind your requirements for resilience and plan for disaster recovery as well - i.e. what would be the impact of a server failing, how would you go about getting a replacement in, etc.

A lot of web server farms and database clusters are justified on the basis of resilience rather than load management.