Hi, can't comment on a lot of your post but can comment on how hard it may or may not be with a newborn and a toddler.
I have five children and when the youngest two were born (twins) my other children we 7, 4 and 2. In my opinion, it is not as hard as some people say. Ok, it was tough at first (but I think that is because I had twins, not the age gaps, and I breastfed them so there was no let up). The upside of having them close in age is that they are natural friends and they are good company for each other. Whilst I anot a single mother, my husband works long hours and I have no family in the area and as i was new to the area, I had no friends to call on for a break.
I hope you make the decision that you truly feel is for the best for yourself, your partner and your daughter. xxx