A chiller isn't a neccessity. It depends on your location and whether or not you can keep the tank cool enough. I personally have a tank in my house which I can keep at 19 degrees celcius all year round without any additional equiptment (It is far from a huge tank as well, the sizes you are talking about are way bigger than the tank in question so would be even less prone to temp fluctuations).
Alot depends on whether you have a cool spot within the house and even then, if you have it fluctuate a few degrees for a few days in summer then there are ways around this without forking out for a chiller. Filling bottles with water, freezing it then letting it float in the tank is one way to keep the temp down, as are fans, etc.
The filtration advantages of liverock as well as the added foodsources it can bring would also make it a huge plus to include in any sw tank, this one included. Do you absolutely, positively need it? Not really. Do the advantages it brings make it worth considering? Defenantly. Excluding live rock from any saltwater tank is not a decision I would make with any degree of lightness.
