I thought you had a 4 year old skin kid you wanted advice about! Duh!! We had another dog who was 3 when we brought Jake home. We actually introduced them first on somewhat neutral space. We took Dena to Jakes house and they met in the front...then we brought Jake home for an hour first..then a week later he came home for good! I'm sure they will love each other! Just make sure you spread the attention on older one thicker than ever! Good luck..and congrats!
So long as your 4 year old is still playful (mine is 5 1/2 and still quite playful) then I would think they should be ok. Make sure you pay extra attention to the oldest and of course that one is alpha, or will want to be so make sure not to confuse the two. Older first with everything. Wont be a problem till the baby gets older but at some point there may be a struggle for power so if you set them straight from the start may save you a headache. I am NOT the one for good advice on training however there are m,any who know the right order of things and how to keep them in the right direction. 
Congrats by the way! JEALOUS!
can't give advice, because we only have one spoiled princess. Can't wait to see pics of both though!
the natives get quite restless when we don't get pix... 
