I saw an adorable dog on petfinder.com that we might be interested in.

Will I have a problem adopting another dog since Gizmo is not neutered?
This dog I am looking at is a female and is already spayed.

Also will I have issues with dominance between the 2 dogs?
They are about the same size! But different breeds and different sexes.

My #1 concern is keeping Gizmo happy. He loves other dogs and would probably enjoy the company of another dog since he is home alone all day, but I don't want him to feel threatened or jealous.

how is he around other dogs? have you ever dog sat another dog with Gizmo around?

we didn't have too much of a problem because Bailey was raised with another dog, then was around another dog when we were living with SIL, and then we got Boomer. But bailey is spayed and so is Boomer.

There might be some tension in the beginning, and if you are adopting through petfinder, the agency might let you do a trial with the dog for a few days or a week so you can see what happens!

There will probably be a transition period during which Gizmo may be jealous and even have some domination issues. But I'd say they'd settle down after a while. As long as you pay equal attention to both, you should be fine.