Can someone recommend a tall, quick growing tree that's not overly invasive that would serve well to plant around a backyard to help break the line of sight of neighbors into my pool / backyard?
Where I used to live everyone did Leyland Cypress. The are fast but not as dense when young as I would have liked. I found Thuya plicata 'virescens'. They provided screening instantly at 8'. They are a variety of our Western Cedar that grows more narrow and yet very dense, very dark green. They are much better in the wind than the Leyland oddly enough. In 5 years they were 15' and 5' to 7' wide some as close as 5-6' apart. I never had to shear them and they stayed dense to the ground.
Try not doing a straight line. I like to offset them from each other, grouping them in a more natural-looking way. If one dies, no one will be the wiser. I even like getting a few smaller trees to mix as well as a few understory, deciduous trees such as Serviceberry or Elderberry (the dark purple was gorgeous)! Birds loved these trees. Don't stake your trees if you can possibly help it. They will grow faster and stronger if you don't stake them. Try to dig up the whole bed you will be using for plants. If you are removing grass for this bed use it to form the foundation of your bed just stack the chunks upside down and top with 6-8" or more of good topsoil. Plan it so that the rootballs of your plants sit on undisturbed soil and keep soil away from the bark of the tree.
Thuja "Green Giant," worked for us. It grew about a foot a year and blocked out the neighbors really quickly. Although it does grow REALLY tall. https://www.youtube.com/watch?v=qaHrOYx1w4M