You guys will be fine! I traveled quite a bit with my son starting at three months (our first trip by plane and it was to Mexico). He was a pretty intense baby (and now kiddo), and somehow, travel always worked out fine. I would guess that you are going to be pretty surprised by your baby's ability to roll with it all!
Honestly, I wouldn't worry too much about germs. How do you handle germs at home? Aside from obviously not handing your baby to a sneezing feverish person, you can't avoid them.
You can't really preserve her sleep. Being in a different place, a slight time change, going to events that require you to be present when she would normally be sleeping, etc all mean that it will be thrown off. I have always felt that the travel, experiences and relationships are worth a messed up sleep schedule for a short time, though! I still find that my son is so tired from all of the interactions, everything being so new, etc that he sleeps in places and at times that he normally wouldn't if we are at home doing our regular thing. She may just crash out in the car because she is so tired.
Food - you are her mama, so you get to pick her food and feed her. I would just calmly tell whoever is offering "suggestions" something along the lines of "oh, thanks. we seem to have figured out a system that works for us..." and sort of blow them off.
What was most important when we were traveling was paying attention to my baby's cues and responding. Notice if your baby is tired and needs to sleep, if there are relatives she really likes or dislikes and either promote or protect their interaction, if she is starting to seem overwhelmed, take her away for a bit, etc. Also, I think that carving out some down time each day is a great idea. I don't think it has to be set in stone, but would try to find some time each day where you guys could have that quieter time. I think that if you listen to her and respond, she will do great! Have fun and don't worry too much!