Hi syndicate1, it was also one of my dream destinations. I visited a few years back in March, so not long before your time.
The most important thing I did was nothing to do with equipment - it was to visit the site twice, once on the day of arrival, and again the following morning. This gave me two chances with the weather, and the morning visit means you'll have some time before the day trippers arrive - it really was MUCH quieter the next day. Likewise staying overnight also means you can stay until the very end on your first day, again making it quiter with potentially better light.
Here's my favourite shot taken at closing time on day one:
I also got some good snaps in the 'food court / market' in the little village below, along with some good food and drinks.
Both taken with a full-frame Canon 5D (Mark I) with a 17-40mm lens at 17mm - so, very wide! That Alpaca was just a few inches away from me!