OneView will run on a virtual Windows server with 4 CPU cores 8GB RAM and 100GB data disc. That is all you need to get started. 

Should I have one or more OneView servers?

Most OneView systems can be run on one server. The OneView software is several autonomous components that can be installed on separate servers. In this way you can distribute your data collection onto several OneView servers. One server might make CPU hungry scripted tests. A dedicated log reader server may be installed at your outsourcing partner for security reasons. The log reader server access the log files and sends response time data back to your central OneView server.