hmm,,, well it's my understanding that if you fertilize before overseeding the old grass will be growing way too fast and you will be faced with having to mow it when you don't want to disturb the new seedlings. A reel mower could be used for that problem (used off craigslist for $20) It's also good to cut the existing lawn very short but not at once (take off 1/3 at a time wait a few days) and it will "stunt" it's growth and give the new seeds better chance to get to the soil. I don't think the new seed needs any fertilizer for about 3-4 weeks, all the food it needs for that time is in the seed.

you will need to do some more research, i am not 100% sure

Any other opinions? My guess I need to start over, its been a brutal summer.

I would not fertilize again until end of October, but I would not wait much longer to over seed. Do some overseeding, it can only help!

From what I understand about 'starter' fertilizer it has a higher degree of phosphurus---the middle number---and lower than usual amount of nitrogen...the first number so to prevent growth of the resulting seedlings until they gain some strength. I don't believe what fertilizer you used...20/10/10....is a type markeded as 'starter' type.
I've never used a type such as this, haven't had to 'fix' a lawn but I have regularly overseeded my lawn in both spring and fall....and overlayered a topping of compost as well.
I think there is a question of whether cutting a lawn short in the fall does any good. Yet many do and swear by it. In New Jersey there is still plenty of time to overseed a damaged lawn and bring a new lawn into existence.

How much compost for 5000 sqft ? Does it make a huge difference to use a slit seeder opposed a broadcast spreader?

Thanks

SLIT SEEDER/BROADCAST?

I have never used a power seeder, but I know some who did. Seems like the biggest thing is to dethatch first. Otherwise the power seeder will pull up some thatch and make a mess of things. I opted to broadcast my new seed yesterday. I ran my spike aerator over the lawn many times first so I had plenty of moist dethatched soil beneath my existing lawn

Seed needs to be in contact with bare soil in order to germinate. Broadcasting can be a waste of money unless it can contact the soil.
I would always choose slit seeding over broadcast seeding!