Hi and welcome to the board! Glad to have you here.
First, let me say good for you on immediately changing your bad habits.

It'll definitely help.
I've had five children and they are all happy and healthy. My biggest advice is to get to your OB or midwife and get on a pump. I swear had I had the opportunity to pump while pregnant I would have done it in a heartbeat.

If you'd rather not have a pump, Lantus and Humalog are perfectly fine for pregnancies.
Eat healthier. Regarding "eating for two", well I never did because I had severe hyperemesis the entire 9 months for two of my pregnancies, so whatever I could get into me, that wouldn't come back to haunt me, I'd eat. Like I said before, just eat healthier. You might want to see your endo and listen to their recommendations, maybe even see a CDE and/or nutritionist to get a good baseline going.
Congrats on the pregnancy, and again, welcome!