1. I prefer to aerate in the spring. If you aerate in the fall there are leaves falling.
You can aerate whenever you like actually. Obviously you can't do it when the ground is frozen. I prefer spring because that's when the grass is starting to grow
2. Seed after you aerate. That way seed will get into the aeration holes too. If you seed before hand, the seed will get all over the aerator tines.
3. Don't do a pre-emergent until the spring if you have to, well after you have seeded. A pre-emergent may not harm established grass, but it will have an adverse effect on seed germination. By the way, if you have a healthy lawn alot of your weed problems should go away naturally.