Im wearing the same Paige booties, but you could also wear a pair of brown ankle boots, black booties, heels, sneakers, sandals, etc
Many people can opt to wear a backless brausually, it's for the look when wearing a backless dress or low-cut silhouette
I woudl say there a touch short but its fine
If its windy, pick a gown with a little weight so youre not holding it down the whole time (or flashing the photographer)
For nursing-friendly dresses, I recommend shirt dresses that unbutton (maybe one size up if your chest is bigger than your pre-pregnancy size) and smocked dresses like this years ubiquitous nap dress (which actually satisfies tae very rare trifecta of looking good when youre not pregnant, pregnant, and breastfeeding no small feat!)