We currently have a 5 yr old maltese shih tzu mix, and are planning on purchasing a golden retriver puppy. Our?

we will be moving into a new house recently purchased and want to add the puppy asap. My logic is that our dog is very territorial and to be honest not very friendly to people other than my very close family. He has grown up around other small dogs and get along for the most part, but I feel if we get the puppy as soon as move into new place, he wont have time to claim his territory. Also him being a male(is fixed) is it better if we buy a female puppy or another male?