As far as I know, there is no mention in Quran about not doing business with, or not hiring, or not working for, non-Muslim people. So, I take it as allowed, as long as the business/work is not haram in its nature.
If doing business with, or hiring, or working for non-Muslim people were forbidden, I would think there would be a mention of it in Quran. In my opinion, it should be encouraged to do business, hire or work for non-Muslims, as it is one of the ways for Muslims to show/explain Islam to non-Muslims.
As for eating from food a non-Muslim cooked/prepared, Quran verse 5:5, as far as I understand, tells that:
1) all the good/clean foods are allowed, -except things that are mentioned in verse 5:3, and as long as the food is obtained and prepared in halal ways-.
2) the food of the people of scripture (Ahl al-Kitab) is allowed to Muslims, and the food of Muslims is allowed to them.
As far as I know, there is no mention in Quran, about not eating the food (as long as it is halal food) of people other than the people of scripture. My understanding is that if eating the food of people other than the people of scripture was forbidden, Quran would have mentioned it.