New arduino user, seeking guidance on thermostat project

I'm looking to build my own thermostat with multiple temp sensors and lcd with buttons. I have never done anything with the arduino unit however I know multiple people have done this exact thing. The code I hope to write most of it my self. I want to start getting some hardware but i'm not sure what all to get to start with. Here is what I plan on doing:

-finished project will be ethernet connected -control HVAC/Fan/Heat -run on a schedule -log power on/power off of hvac fan heat as well as the temp of the house either onboard or to an external server or both -3 seperate temp in 3 rooms and average the temp for a better reading -LCD with ~2 buttons (maybe a switch to shut off all cooling/heating) to display current stats as well as temp change to override schedule. -an alternative is an LCD screen with a touchscreen overlay as the interface ~pull power from current line for power and save settings to eprom but have a battery in case of power failure

This is what I have questions about: -Will I need more than one arduino unit? -What kind of unit(s) will I need? -Should I go with a larger unit to allow for a small web server (not sure what the limitations of the arduino are)?

Make a plan and do one step at the time.

Start with spending one evening at the tutorial and reference section working through the examples, you will learn a lot from it and you will find usable pieces of code there.

Check out - http://www.ladyada.net/make/logshield/ - it can give you some ideas

This is what I have questions about: -Will I need more than one arduino unit? -What kind of unit(s) will I need? -Should I go with a larger unit to allow for a small web server (not sure what the limitations of the arduino are)?

1) No it is doable with a UNO 2) UNO 3) no not needed, however a Mega is fun too.