D.W.
One thing to take into consideration when planning for a second is how hard it may or may not be on your daughter at that point in time.
Our kids are 21 months apart. Our older did beautifully transitioning to a younger sibling. My sister had her 2nd last week, and her 26 month old is having a tough time. A lot of it is personality, a lot of it is getting accustomed to being the "baby". How you approach the one-on-one time with a 2nd is also a major consideration.
None of us can tell you what's right, but we can encourage you to follow your instincts and to do what's best for you. Money is always a concern no matter how much you make or how little you have. It's always a stressor, and people figure out how to make it work.
I'd like a third. We're not in agreement about it for many reasons: money, time for us, having been diagnosed with cancer after the birth of our 2nd, off number of kids, etc.
Good luck with your decision. It's a tough one, and you'll make the right decision. A lot of the moms here with 3-4 kids still don't feel complete when the realization of no longer having a baby hits. It's probably very common and very natural.