As low as your mower will go. It will be be fine.

Yeah you want to go low, and id bag it if you can because you want the seed getting down to the soil and not laying on the grass. 2" is what I would think

Is it still recommended to use the bagged clippings as a topdress for the seeds?

It's not always necessary to cut the lawn as low as your mower can go but it usually makes overseeding more effective. I would also recommend feeding your lawn seasonally to ensure that the overseeding process is as effective as possible. Feeding your lawn with a limited amount of fertilizer helps strengthen the roots and helps your lawn recover from harsh weather and pests more easily. Other than that you're on your way to a lush and healthy lawn!

Is it still recommended to use the bagged clippings as a topdress for the seeds?

I would. It has helped with establishment.

I had a thought last night - what about seeding right into the grass and then using a reel mower to cut the grass right on top of the seed? I think a rotary would be risky, you can suck out all the seed, but a reel would just dump the clippings right on top of it. Then you wouldn't have to take the clippings off, put them back on etc., a lot of work saved.

You know j4c11, I had exactly the same thought just the other day. I'm too scared to try though working with half an acre. If it doesn't turn out well I'm screwed.

Why the reel? Could you just mulch mow with a rotary after seeding? Seems like that would also help distribute the seed evenly

@reeljake

I would be concerned about the mower sucking up and damaging the seed, especially with fescue where seed is fairly large. But I guess if you stick the mower into 4" tall grass on mulch, it may be too loaded with grass to suck up any seed. It would be worth testing in my opinion, could save a lot of work and be great for germination. Maybe I'll do a test area next year. But hey, I got KBG now, no need to overseed ever again, right ? :-)

I guess I was picturing Bermuda seed, which is so tiny the suction would barely grab it & the blades would probably never touch it.