P.,
I'm going to add my opinion that cereal should never be added to a bottle! All the current research supports this so if you received this advice, it was probably from someone that parented before the advice changed.
Having said that, I have a son who will be 5 months old in a week and a half. He still gets up at around midnight and 4 am. (Part of this because he goes to bed at 8 pm and sleeps until 8 am and I should tweek his schedule.) All babies DO NOT sleep through the night! I'm back working full time now and it's exhausting, but it's what he needs so I do it! My first child did not sleep through the night until she was 9 months old and I guess I'm not expecting anything this time, which probably makes it easier to deal with.
Hard as it may be ~ ENJOY those quiet middle of the night cuddle times!!! They will soon pass and nothing really replaces how quiet the house is in the middle of the night and the warm snuggling and pure comfort that you are providing to your little one in the wee hours of the morning! If you keep disruptions (no extra lights, no diaper changes) to a minimum, I can do a feeding in about 10 minutes and we both go right back to sleep.
As far as feeding, I started my son off last week with 1 TBSP of cereal mixed with enough breastmilk/formula to make the cereal loose. If your son is good with the swallowing and having the spoon in his mouth and seems to want more, increase accordingly and thicken the cereal. Start once a day and add a feeding when you feel ready. Pretty soon your son will also be ready for you to add Stage 1 veggies and fruits to his diet, too. (I usually did these at lunch first and kept cereal for breakfast and dinner.)
Good luck... and enjoy all the moments!