Hi guys,

Looking to get a new internal frame pack..Any recommendations? I am also not too sure of the size. How many litres will I need? Will be going to Peru for 2-3 months in Spring - doing some volunteer work and hiking some trails, including the Inca Trail...

Having worked both in the field and in retail, I'd suggest you have a look at Macpacs or WE packs. Not cheap but well worth it as they will last you a lot longer than their cheaper alternatives.
Something around 70-80ltrs.
If you need more advice, go to a store, but not just any camping store (I'd avoid Aussie Disposals and Ray's Outdoors as they specialize in car camping) Paddy Pallin and Bogong would be my pick.
On a personal note, I've got a North Face Inversion 80 that I'm absolutely delighted with, but they're hard to come by in Oz.
Good luck!