Do you have creat a webserver or just send and receive comands using ethernet? If you need webserver, get a processor core and a ethernet core (or an exrternal ethernet controller). If you dont need a webserver, you dont need a processor. Its kind hard explain without solving your problem, but al you need is a ethernet controller (external or internal) and a parser of the messages received for configuration and a block that create your message with the sampled data. The most easy solution would be get a SPI core from opencores and use a microchip ethernet controller. Creat some internal protocol for your control and get all the data and put on the ethernet controller using SPI.
Cya