Mowing is normally recommended for the first year to keep weeds from hogging all the sunlight. Young native plants are small the first year of seeding. As ozark said, they spend the first growing season putting effort into good roots. It is said that native plants SLEEP(year 1), CREEP(year 2) and LEAP(year 3). If you can keep the weeds at bay for the first year, you should be OK. You won't need to mow forever. I have a couple of patches and really don't need to do anything to them any more. If you can burn them every couple of years that will help the stand and get rid of too much thatch.
See what the patch looks like this year without doing anything. I bet it will end up looking really good!
