I'm a fuel-as-I-go kind of guy. I'll have a light breakfast, then take gels at 6, 12, and 18 miles. Pace-wise, I try to maintain a consistent effort, but I don't stress too much about speed. Walk breaks? Nah, I'd rather push through and get it done. That being said, I do make sure to slow down for water stops. Currently, I'm doing 20-milers with a goal of getting to 24 soon.
I've tried both approaches and honestly, it depends on your fitness level. If you're not properly trained, starting fast will only lead to a miserable second half. Aim for a consistent pace that you know you can maintain, and then give it a push in the last 2K if you have it in you.