Magnolias like acid soil and so you will need to amend the soil quite a lot to keep them happy. They will not appreciate local water as it tends to be alkaline. If you want Magnoila, get the smaller leaved varieties like Little Gem. It tops out at about 18'. I just visited the Dallas Arboretum and was amazed that they had so many azaleas and camellias and magnolias, it is almost misleading as they work quite hard to keep the soil correct for those plants. Not many homeowners can do that given the local soil. My daughter's yard was full of big rocks in Ft Worth, not sure if Dallas is quite that bad.
My advice for using tropicals is to create a triple border. In back, taller evergreens - some sort of shrub of the mature height you want there. In front a short evergreen, maybe liriope or a holly fern if it is shady. Then in between plant the tender tropicals like cannas or gingers or things that die back in the winter. When they are gone you won't miss them with the other greenery but when they are up and blooming they will be the big show.
I have a regular Magnolia behind our pool (I would not have placed it there) as well as several others in the yard. They are mosquito breeding zones when the fallen leaves collect rain water as they are shaped like little boats. The flower cones are very unpleasant to walk on and must be raked before mowing. Then the flowers, though lovely, are too high to cut for the house. No, not my choice of evergreen for the pool area. Though they do screen the neighbors the fast growing wax myrtle does that just as well without the problems.
As for palms, just be sure to keep them far enough from the pool that they do not interfere with the pole on the pool brush. Hard enough to brush the pool on that landscaped side without nearly being thrown in when the pole gets stuck in the palm tree.
