My project=Greenhouse--what do I need?

I am trying to automate my little greenhouses, & arduinos sounded like an interesting & possibly cost-effective way to do it.
TASKS/SENSORS: max air temp, min air temp, min soil temp, air humidity, soil humidity---extra: motion sensor, pH,
OUTPUTS: louvered vent fans, air heater, soil heater wire, circulation fan, watering mister, drip irrigation, display, & interface---extra: web interface
Once I get into it, the half-breed geek side of me might get carried away with it. But for now, I want the simplest, easiest, & cheapest way to go about it. I am reasonably computer literate, but don't know any computer languages well, but it sounds like I could figure out this OS. If not, I have some kids who can.
Suggestions on which arduino to use, etc?

I'm new at this, but if you have all those sensors/outputs you might want to try the Mega 2560, because that microcontroller has a lot more places to plug in sensors and other components. Sometimes on the Uno I run out of pins to plug things in, either that, or things just get really crowded.

If you're new, I think you better start with something small, and get something working. Pick one sensor that you want. Then, add more as you go along. I think that project is going to be way too big for someone just starting. It would need to be done in steps probably.

With the Mega 2560 that's not hard to do, because you have plenty of room to expand in the future.