I reckon the garmin on auto lap is going to be pretty similar in accuracy to any course markers. Although the actual finish line is going to be in pretty much the correct place, mile/km markers are quite often a way off - usually bunged on the nearest bit of street furniture. Just treat either of them as a rough guide.
Regarding screens, I have 3 - Average pace, distance and large time.
In a five miler it is going to be pretty intense and you are going to be pushing it pretty hard more or less from the off, so I wouldn't bother too much - just a quick check at the first mile marker that you haven't gone off at a bonkers pace! The only time I would possibly look at my heart rate in a race is possibly in a marathon or longer to help me run the first miles slowly enough, but I think even then I'd just use pace.
I use average pace as current pace is all over the place, and not much use at all. I do have lap pace showing on one of my other screens, but have never looked at it in a race. Average pace, does mean I have a really good bit of info for predicting finish time - I have my A-goal, B-goal and C-goal pace firmly stuck in my head when I set off.