If your wife doesn't already exercise, she should start. Even just a 20-30 minute walk after meals is a solid start.
As far as the prenatal diet, there are, to my understanding, two important elements. One is folate. The other is maintaining a healthy weight. Your wife isn't eating for two, she's eating for 1.1 or so. Although the crave-induced trips to the ice cream shop are fine for movies, being overweight is associated with complications during pregnancy and delivery. Not a doctor, this is just what I read as I read up on this during my own wife's pregnancy.
Early child rearing is pretty damn basic. Feed the kid as much as they will eat. Breastmilk is best, but formula is better than not having enough. They sleep better when well fed, so it can make the first few weeks a lot less hellish if you have some formula on hand if your wife's production isn't up yet. There's not anything else to it for at least 15 months from where you are now, so I wouldn't sweat those details yet. You'll have more than enough to deal with between now and then.
To err on the side of cautions, minimize the use of TV screens in the room where the baby is hanging out, even as background noise.
Hospital-grade breast pumps are more than worth the $90 rental fee. Even better if your insurance will pay.
Do whatever you can to resolve any conflict anti-patterns you have with your wife now. This part does not get easier once the baby arrives.