I am completely new to this concept, traveling south america that is...

Doing a career break at age of 28, have unlimited time and solid budget, planning to head of at end of September or beginning of October, the reason I'm thinking of going to south america and not to the far east is - no particular reason, can't say I'm an extreme sports lover, I like mild hiking, good views and food
Currently worried\not about the following:
1. Suitcase or backpack? I of course prefer trolleys but if there is no pavement - this would not make a lot of sense....
2. Mosquito - I'm terrified by this more than by anything else, I'm one of those people that get bitten everywhere and by everything and completely allergic to them... what would you advise other than using repellent? Special areas\seasons to avoid?
3. Company - I'm traveling alone... will I be that lonely...? Is there anybody there that I can potentially exchange impressions with after...?
4. Route planning - I'm going to start in Peru, just because I found a friend who wants to join for the first couple of week and have no idea what to do after....
5. How to make sure that I stay in somehow reasonably comfortable places... meaning no dorms, clean sheets and hot water
6. I'm booking the flight with award miles, how can I still get air passes?
Thx a lot and my apologies for many basic questions
