Oh what fun a new puppy. I have 2 boys and a girl. The boys are way more cuddly and affectionate then Pebbles. But she likes to rule the roost.
I don't think you need to worry too much about introducing a new puppy to a 5 month old puppy. When I brought Doodlebug home Pebbles was not happy. She drooled for days and would stand back and do a really odd yapping at him. She eventually stopped. When we added Bogey it was just am immediate bond between the boys. They are still fast friends.