S.R.
Hello J.. I was never one to set a schedule with my babies. I HATED that the hospital nurses would wake me up to wake up my sleeping baby to eat. I thought How Absured lol. I say, let the baby sleep if she is sleeping, when she is hungry she will wake up. It seems to me that she might have her days and nights mixed up. She is sleeping in the morning instead of at night. If that is the case, you just need to wake her up in the morning at (for example) 8 am. Keep her awake as much as possible during the day..lots of diaper changes (even if you leave the same diaper on, the removal of clothes and diaper are suppose to help wake the baby up). If she is eating and fallin right back to sleep (or falling asleep while eating) seems like she isn't really hungry, and eating does tend to make babies sleepy: so I would try to get her to be awake prior to eating and changing her diaper after she eats (expect for when she is screaming to eat :) so she will wake back up. I wouldn't be conserned now with an 'easier transition' for going back to work since you don't have a job lined up or know what type of hours you would be working. Seems you can't really predict what time she would have to get up when or if you go back to work.
For a few days, while getting her days and nights back on schedule, I would avoid running errands b.c the lull of the car generally puts baby's to sleep. Let her sleep at night, keep her awake during the day as much as possible, decide when you want her to nap and let her nap at those times. That is the best advice I have.
Also, I don't think 3 months is too young for baby cereal, and I don't think it will hurt her, my now 5yo had to have (under medical advice) cereal in her bottle at the age of 1 week. 3-4 months is when I always started spoon feeding and cup drinking. Also, with weather changes babies tend to require more sleep. Congrats on having a new baby, remember the 'sleep all the time' stage ends quickly and you will miss it :)