Answer: To answer your questions specifically:
1) No, I don't think you're missing out on anything by cutting back in October. The reason you wait for that first hard frost, is to be sure everything has truly set its seed and is ready for dormancy. It's simply a good indicator--but many plants shed their seeds well before that.
2) Wildflowers are "weeds". They will really do better in poor soil. They should never need to be fertilized. That may generate lots of green growth at the cost of flowers! Once they are well-established, they generally flourish on neglect.
3) I don't think sowing seed among the present plants will work. I've tried that and was totally unsuccessful. What you could do is roto-till "lanes" or "circles", or "whatever" within your meadow and plant fresh seed there. Then each year do that again, but in a different place. Also, I would recommend that when you purchase new seed that you get Perennial seed ONLY!
I hope this helped a bit anyway.
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