1st 5k! Need some advice?

Hi! So my first 5k is tomorrow morning at eight am, and luckily the weather is at supposed to be in the low seventies. However my problem is that I'm typically an evening runner since it has been 90 degrees or hotter all summer. Although I have ran in the morning while training I don't have a set routine. What should I eat, and how should I warm up? Another problem is that I increased my mileage from running 3 to 6 miles a week to 16 miles last week. I learned my lesson though and my calves were so tight the last two runs that they turned incredibly painful. Do you think that since I rested my muscles for four days I should be okay? Thanks. =)