Since you are overseeding you want to use the starter at the very least. Starter is high in P, which is primarily for root growth, important for new grass. It is also pretty high in K, which is also important for seedlings. Most starters contain a fair amount of N as well, it depends on the brand but usually it's in the 16-25 range. If you use the starter at the full bag rate, you can use a reduced rate of the fall fertilizer to get more nitrogen if you want, but it's probably not necessary since you don't want your existing grass growing so fast and lush that it will out compete the new grass.

I would fertilize now and then mid november.
If you already purchased fertilizer, it is fine.
I don't use starter fertilizer, just lesco or scott's turfbuilder.

Ok, I think I'll go with the starter fertilizer now. Then in mid-November I'll put down the regular application of fall fertilizer (well after the existing grass has rooted) which is the recommended timeframe for my area.

Since you are overseeding I wouldn't put your last drop down that late. It's fine for established lawns, but with new grass late fertilizer drops can increase the chance you get snow mold. Mid-october would be a better time to lessen the risk of disease.