You are really brave. I did this with only my 17 mos boy and it was very difficult. A few small tweaks would have helped.
When buying tickets, know that most int'l airlines charge for lap-babies. This doesn't mean that they supply any food for your lap-baby. They are supposed to put you in a bulkhead seat with access to a bassinet, but paying for it doesn't mean that they have put you there. Also, despite what they said, I would say that the bassinet was too small and shallow for a baby older than 9-12 mos (my little guy is smallish but it was ridiculously too small--think grown-up in bathtub).
For such a long flight, I strongly recommend buying him his own seat.
Make sure that you have easy access to the aisle.
When packing toys, divide them into smaller bags for use during 2-3 hour chunks, then put them away and pull out the next bag. Bring a few new toys and pull them out as a surprise when needed. Make sure that your seats have inflight entertainment (not all int'l airlines have it) otherwise bring an ipod or dvd player so that your little girl can keep entertained.
Bring benadryl. I would normally never recommend this. But your little ones will need sleep and may not be able to get comfy/relaxed. it will also help with the time zone shift.
For travel abroad, you may want to pack all the diapers you'd need. Even the same brand may have a different fit. You can buy wipes there. Pack a small first aid kit for your diaper bag with tylenol, alcohol wipes, bandaids, neosporin, sunscreen. You probably won't need it, but it is good to have it.
Not all countries have diaper changing stations. Be prepared to use toilet seats (lid closed) as improvised changing tables.
Depending on where you are going, a stroller may not be useful. Old cities have lots of stairs and rough cobbles. You may be better off with a baby back pack.
If you need laundry, look for a wash and fold service. It will be much cheaper than having the hotel wash anything. Most of the time, you can drop it off in the morning and have them deliver it to your hotel. You can ask at the hotel for a recommendation.
The key to having a good time is being prepared so that you just don't have to spend time figuring stuff out and can focus on fun.