The most commonnly used are the Uno and the Mega. The main difference in practice is that the mega has more pins (ports to use for input or outputs) and more memory. Uno has only 32kb for code, mega 256k. I dropped a few links in this or another thread (search my username for "instructables") to cheap chinese starter kits that are imo the best way to get started with arduino. $20-30 and you get the arduino and a whole bunch of sensors and wires, resistors and other typical items. Depending on how much you want to attach to it (as in how many pins you need) an arduino Nano can work great for a finshed project due to it's small size and price, as little as $5-6.
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That would do for dimming for a few drivers, temp and humidity sensor, timer and relay.
In any case, get the so called prototype shield for the uno (fits mega too).
Yeah, more than you will ever need. For example:
http://www.instructables.com/id/Arduino-Projects/
https://learn.adafruit.com/category/learn-arduino
https://www.arduino.cc/en/Tutorial/HomePage
And many many more. There are libraries and sample code for pretty much all sensors and other outputs and inputs. Lego for adults. The coding is as 'basic' as coding gets.
