Advice for 2nd time mom

I'm expecting my second in 3 months, and my son will be 18 months old at the time. I'm starting to have horrible anxiety about taking care of 2. I'm a stay at home mom, but my husband is a huge help. Does anyone have any advice - routines that worked for them, things they couldn't live without, tips for keeping your first not jealous, etc? Especially for the first few months. I had horrible PPD with my son, and didn't even feel human/couldn't function for the first 4 months. I can't imagine having a toddler to take care of if that happens again.