C.M.
Not going through this (other than the cramped space issue and daycare cost of having another) but I would weigh your pros and cons.
If you go to school, your baby will have to be in daycare. If you don't, you can stay home with him/her and maybe take fewer classes.
If you add another now, you may not have as much money (but if you aren't putting the baby in daycare, it's really just about diaper cost and formula if you do not bf). If you wait, you will be closer to advanced maternal age, which comes with some risks (not always, but more common after age 35).
Most importantly - what do the two of you both want to do? Are you on the same page? And also, I would not rely strictly on the plan that 2 months after you taking out the IUD that you would become pregnant.
All that being said, if I were in your shoes, I would take out the IUD, kick school into high gear (taking as many classes as I could) and do that until the baby were born. Then I'd plan to take time off with the baby (even a semester if that is what you need to do) and maybe get a part time job while hubby is home so we wouldn't need daycare. Then you could see how much schooling you have left and see what your best options are.
You are right that you will never be 'ready' financially for another unless you are a millionaire!!
In our case, we'd like another but I do not want another one in daycare (we have two currently) and want a bigger house. So for that to happen, I want to either move or add on and then have my daughter be at least 4 years old (so if we did get pregnant right away the baby would be born the summer before she goes to Kindergarten and I could keep her home that summer in order to save on daycare costs).
GOOD LUCK!