If I have rosacea, should I avoid certain foods?

Yes. Although food triggers for rosacea can vary from people to people, but the common exacerbating foods include caffeine (coffee, tea, chocolate), hot spicy foods, alcohol (especially beer and red wines), etc...
No need to avoid. You don't need to avoid foods, but you you should know that alcohol and spices will make the redness more pronounced for a short period of time, just like a sauna will do the same. Good luck from nyc.