Hi Dawn,
I know you'll love getting to be at home with your son! It's a huge decision to make, giving up the second income. You will be amazed at the ways you'll discover to save money and make it work. I've been home with my daughter for 3 years now - never thought we'd be able to swing it, but it's going great and I love every day!
I think most babies start cereal around four months. My daughter tired it and didn't like it, so we waited. By six months she was ready. I would encourage you to use organic foods as much as possible for your son. I know they cost a bit more, but the peace of mind you'll have knowing you are giving your child the best start possible will be worth it. Earth's Best is a great brand and you can get coupons from their website.
Here is a link with guides to shopping at consigment stores and a list of some consignment stores in the Dallas area.
http://www.dallaschild.com/featuredetail.asp?ContentID=613
If you're at Babys R Us or some other child-oriented retail place, you'll find free copies of child-related magazines. Most of them will having listings of consignment stores. Sometimes the shops will offer coupons. I think they are great places to shop.
There are also some seasonal children's consignment sales that take place in spring and fall. There is one this week, Tuesday and Wednesday in Frisco - not sure if that's at all close to you. You can check out their website at www.threesistersconsignments.com. I have sold my items with them for a couple of years now. Very nice ladies, lots of great stuff.
You can probably google "consignment sales dallas" and find others too. This is the season!
Best of luck...
N.