Hiya,
I have the above combo; a nearly 4 yrDS, a just 2yr DS and a 6 week old DD. I can honestly say that the move from 2 to 3 was not as hard as the move from 0 to 1 or 1 to 2 kids. DD just slots into the chaos (now we are very chaotic but the two boys do that all by themselves). If you can manage 2 then 3 are not a problem in my recent experience! And also, i am so relieved not to be pregnant; i am managing better now the baby is here than i was before. Tips? none, would love some!