Have your own finances in order. The rest will work out. I also highly recommend that you don't go too heavily into baby podcasts/down the Internet black hole. You'll just make yourself crazy!

If you say married filing jointly without going to the next steps they assume you are the only income earner. Taxes are withheld so that it is like that is the only income for two people combined versus each having an income and therefore you end up under withholding.