Coffee is fine, milk has sugars so depends on the amount you're talking about and how much it takes to knock you out of ketosis. Probably better to keep consumption withing your eating window. My energy levels are super stable. No peaks and troughs. The key is to listen to your body. Eat when you actually feel hungry and don't be a slave to the clock. Sometimes you'll not feel hungry at 12 so delay a little that day and get extra benefits of a slightly deeper fast. Some days you'll feel hungry at 10 so just eat and don't feel bad about it. Instead examine what you ate the day before that meant you didn't consume enough calories to get you through to 12 and adapt.