I have a 16 month old myself and "one in the chamber." That means my wife is pregnant with our second.
But seriously, congrats on the new one. Children are the greatest joy.
1. I recommend your wife try hard to breastfeed. It's best for the baby and it's God's way of mommy working off that extra maternity weight. It will be difficult to stay on top of pumping, but she needs too. If your wife stays on top of it, she won't have any interuptions in milk supply.
2. As mentioned above, it doesn't matter if you have 6 months of formula or 6 truckloads. If the kid doesn't like it, then they aren't eating it. End of story.
3. Again as mentioned, spring for the car seat. Pretty much everything else is fluff. I can't tell you how many times the cheap items were actually better. My son prefered the crappy $30 swing compared to the $200 one. Same with cloths. If you don't want to buy from Goodwill, look for bargains. Costco has outfits for around $8 and it gets you the shirt, pants, and shorts. Buy larger outfits for the future! My son might be in 24 months, but we have several items in larger sizes. They grow like weeds.
4. Same as above for furniture. You don't need the $400 crib and $250 changing station from babiesRus. The $100 crib works fine for me.
5. Diapers. Find the brand you and your wife prefer. We like Pampers. Unfortunetly, Costco doesn't sell that brand; but BabiesRus has specials on the bulk packs from time to time. Sign up for they're promo card, you get good coupons in the mail. I bought two boxes this afternoon (It'll last about 7-8 weeks) and ultimately got $18 off ($4 off each box for coupon from mail, $10 gift card I recieved from last purchase of diapers) and still got another $5 gift card for next time.
Good luck with the new one. Remember! They'll sleep through the night soon enough! :)
Jeremy S.