Wow! He's here already! Time sure does fly.
My big tip for baby's first trip to WDW is to invest in a nice umbrella stroller! We spent a small fortune on a Peg Perego (it had to recline all the way for sleeping, have a full hood to protect from the sun, and fold up small enough to fit in an airline overhead. It saw 4 trips to WDW and broke once my oldest became just too big for it! We bought a replacement Kolcraft at JC Penney for less than half the price for our younger son. It is almost as functional but needs to be gate checked. The colors are cool gray, black and yellow. Fits right into the stroller parking at Test Track!
Congratulations! Stay in touch during those late nights up with the baby!