There are certain vaccines you need to get before going (coming from the states). I had a card with me that the doctor gave me with what I got in case I needed to show customs. I forget where I found out I needed. Guide book, doctor and/or countries (tourist) website. If memory serves, I got Yellow fever, Typhoid, Rabies and maybe one or two others.
I was a little worried about my belongings, but in the end I/we never felt threatened in any way, anywhere. The usual rules apply. Stay aware, keep things close, put your wallet in your front pocket and you should be good. We did have a couple pieces of clothing that had the inside pockets for really important stuff (passport, CC that I wasn’t using but didn’t want to leave in the room). Again you are going to a major tourist area. There will be tons of folks with DSLRs and other gear.
Get travel insurance that offers evac to a country with better hospitals. We didn’t need it but it’s better than ending up at a local hospital.
We didn’t have a human guide for the ruins. We did have a book that we referred to now and then. One thing that my friends did in general was to download web pages with the most recent reviews/recommendations/info (WikiTravel, Wikipedia, other travel sites) to their smartphone for reference when needed specially when there was no wifi or phone connection.