For your first half, I would play it fairly conservatively, and stick with a pacemaker who is running a time you are confident of achieving. If you’re feeling good, by all means let it rip towards the end to empty the tank. Once you are more accustomed to your limits, pacing and how it feels when you’re on the edge, push the boundaries. It’s better to have a realistic target which you meet, than an unrealistic one which you fail at I’d say.
I’ve got my first ever 10,000m on the track this evening, not ideal weather with the wind, hopefully I’ll manage not to get too bored running round in circles 25 times!
Cheers, Rich