Certified GKH Gardening Expert
I would recommend applying this after breaking ground. Moss can be very difficult to maintain, so anything that is done to disturb it will usually kill it anyway. Adding a moss killer after will ensure that the rest of it is completely killed off.
It is also important to increase light to the area. This will be the best way to keep moss away.
As far as a fertilizer... Any lawn fertilizer will make the soil quite toxic for moss. Just be very sparing with fertilizer for young lawns. This can be a bit much for seed trying to establish.
This article will help: https://www.gardeningknowhow.com/lawn-care/lgen/lawn-seeding-tips.htm