Marriage is one thing. Parenthood is another. While it sounds like you were both adjusted to married life pretty well, it is now time for both of you to adjust to life as parents. We don't know how we are going to be as parents. We can dream and plan and hope, but until you are in the situation, you just don't know what it is like and how you or your partner will react/respond.
I would suggest waiting on a second child for many reasons - your daughter is only 11 months old (that is really young - give her time to be a baby before she has to be a big sister), you and your DH are both SUPER busy, you do not have health insurance, you have both not yet adjusted to parenthood TOGETHER yet, two children (especially young, and especially close in age) can be a TON of work - more than double! - and can put EVEN MORE strain on your marriage, and most importantly, you just threatened/gave the option of marital separation!
Work on your marriage, work on learning to be parents TOGETHER, work on giving your little girl the best life and love and attention that you can, work on showing her what love is through your love for her AS WELL AS your love for her Dad (and vice versa).
Take time out as a couple for honest, open discussion about roles and expectations that you have of yourselves and each other as parents. Talk about what challenges you as a parent. Talk about how you can support one another in those challenging areas. Talk about how you can utilize your greater support network (grandparents, friends, etc) in those challenging areas.
Parenting is a HARD job! Parenting is the MOST IMPORTANT job! It is a hard role to be thrust into - which is really how we all get to be here, no matter how much we plan. You need support. Your husband needs support. Be there for each other. Seek other help if it is necessary. It is not about you any more. It is not about him anymore. It is about your daughter now. When we choose to have children, we choose to put their needs at the forefront and ours on the back burner. It is a balancing act, to be sure.
Best of luck to you.