I'd like advice about visiting Peru.?

A female friend and I will be in Peru for one week over Thanksgiving. We're going to see Machu Pichu, do some hiking and haven't decided what else. To keep costs down we're planning on sleeping in Hostels. I speak a little Spanish and intend to work on that more. Should I get my vaccinations now? How intensely should I refine my Spanish? Any advice on places to eat or see? Weather? I'd like to take very little luggage .... can I buy whatever I need when I get there? I've never gone on a trip like this before.