The most common Arduino is the Arduino Uno.http://www.arduino.cc/en/Main/arduinoBoardUno
You can add an Ethernet Shield for ethernet.http://www.arduino.cc/en/Main/ArduinoEthernetShield
There is also a Arduino Ethernet, that has both combined.http://arduino.cc/en/Main/ArduinoBoardEthernet
If the code is getting large, you can use a Arduino Mega 2560.http://arduino.cc/en/Main/arduinoBoardMega2560
The ethernet library is getting better and better, but it is slow and doesn't handle bad connections as good as normal ethernet devices.
Using an Arduino as webserver (to display settings and to send commands) is possible. The examples for that are easy.
You might consider good quality 433MHz transmitters (or tranceivers).
If it is only to report temperature and pressure and so on, using 433MHz transmitters is a well known solution.
Suppose you have a number of Arduino Uno's with 433MHz transmitters and a 'base station' that consists of a Arduino Mega + Ethernet Shield and 433MHz receiver.
That way you can see and control everything from a webpage.