Both of my babies were pretty good sleepers (and by some standards, I think they might have been considered "exceptional") but even for them, it seemed that they had some quirky sleep habits, especially around the 4th month, if my memory serves me correctly. I do remember that, for both of them, the 3-4am hour was a restless time. They would wake to be fed but then have a REALLY hard time getting back to sleep. I don't know what it was about that time of the night, but it was troublesome for both of them. The problem really didn't resolve itself until they stopped waking for that feeding and slept all the way through until morning. Hopefully that is not discouraging.
When you say that her routine is what she does on her own, I don't know if you are opposed to a schedule, but you said you were looking for "any/all words of wisdom" so I'll tell you what worked well for us (I know schedules don't work for everyone!) :) I attemped to have my babies on a routine from a very early age, and I found out that it was not a popular notion, but it did seem to be very popular among the "professionals" to start a consistent routine around the age your baby is now. So I don't know if that makes it sound any more favorable to you, but the thought occurred to me that maybe that is just what she is needing right now (as a baby who is keeping her own consistent routine, maybe she is routine-oriented and needs that consistency). If it is something you want to consider, I would suggest falling into her normal self-regulated routine as far as feedings and naps go, and try to keep it the same throughout each day, even if she behaves a little outside of her norm on a particular day.
The 2-3 naps during the day sounds the same as what my babies did, and is fairly typical from what I understand. I used to worry, especially with my first baby that he would sleep too much during the day and not sleep as much at night, but my mom (who had 7 babies) told me over and over again, "the more a baby sleeps, the more a baby sleeps." I always thought if I kept them up longer and got them really tired out, they would sleep better, but it was always just the opposite! When they got overtired, they never slept as well, but when they were getting sufficient rest, they slept better overall. Around 5-6 months they dropped the late afternoon nap and took a morning and afternoon nap until about 15 months, then just an afternoon nap.
For bedtime, 7pm has always been a good bedtime for us (waking at about 7am) but if her current bedtime and eventual morning wake time is good for you, then I wouldn't change it. Otherwise, you could gradually change it by about 15 min every few days, if she tolerates it. I also woke my babies to feed them before I went to bed at night and it worked well for both of my babies (meaning, it helped them sleep through the rest of the night). The thought has occurred to me, however, since you are demand-feeding your baby throughout the day, to alter that with that one night feeding may be unsettling to her. I am not an expert on this, but I wonder if a baby does best on one or the other: demand or schedule, but not a little of both. Not sure of this myself, but just a thought (hmmmm), especially since your baby is typically pretty consisent on her own.
Some people say rice cereal helps, but I tried a little with my first baby and it didn't help a bit. He ended up sleeping through the night before I started him on solids (same with my 2nd baby) - the solid foods did not have any effect on my babies' sleep habits. When I started my first baby on formula, we started with soy and he did not tolerate it, but he did fine on regular formula. If you are giving her the formula only to see if it helps her sleep better, I wouldn't recommend it. From what I know, it doesn't seem to make any difference, and if you are content to exclusively breastfeed, I think that would be best for her (not only nutritionally, but also for the sake of consistency).
I don't know if this has been any help at all, but one thing I do know is that this WILL pass. I know that doesn't help in the sleep-deprived moment, but do what you need to survive and get through this. Hopefully your husband will understand that you can't handle 2 babies through the night on your own. I saw another mom recommended a 3-day sleep program - I would highly recommend that if you are open to it. I don't know about that program in particular, but I have heard other moms say it is great, and it is probably similar to another program that I am aware of and it is very good. It is probably very "routine-driven" so keep that in mind if you are considering it.
I hope this is helpful!