First, go see your ob/gyn and get some medical advice that is unique to your body, regarding nursing and delivery options. We all have our unique experiences, but this is your body and your preganancy, best to be talking with your doctor.
The finances, the housing situation, the transportation concerns... those are real challenges, but not insurmountable. The good news is that you have two older daughters who are close in age, who can play and relate to the challenges of puberty and school, and now your 14 month old will have a new sibling close in age to share many things with because they will be close in age. Your older daughters will be able to help as well, learning to be more responsible for themselves, ie laundry, cleaning their rooms, helping with dinner, etc.
Your husband is probably just as excited and unsure of the future, but the good news is that you're all going thru this together. And together you can make anything happen.
But see your ob/gyn, get on your prenatals or whatever other supplements they may want you on because you are nursing. My first 2 kids were 22 months apart, and I was nursing #1 child when I found out I was pregnant with #2, not as frequently as you are, but we weaned shortly there after. Again, prenatals!!
Congrats!!!