As a devout Christian, I believe that God is in charge of my life. It sounds to me like doing feng shui is interfering with God's plan.
As a student of things oriental I have some familiarity with the background of feng shui. The basic idea is that demons follow certain paths through the world, and certain things can block their paths so they don't negatively affect your life. Thus many bridges in oriental gardens have a sort of jag in them; this is so the demon goes straight and into the water but the man sidesteps it. Feng shui says that sharp corners bring sharpness (negative influences) into your life so they should be softened by plants or rounded furniture. Certain locations are unlucky because of the demons associated with the place. There is the story of a bank in Hong Kong that was doing poorly until someone told them to put their door slightly off the true vertical. This confused the demons and the bank started doing well.
A Christian can not believe in feng shui because the belief gives credence to the belief in many gods, good and evil, working in the world. In Mark 12:29-30 Jesus acknowledge that the most important command was "The Lord our God is one: And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength." Although some parts of the New Age movement would combine oriental and Christian beliefs, they are generally incompatible because of the fundamental difference between pantheism (everything is god) and monotheism (there is only one God).
Is doing feng shui interfering with God's plan? In one sense, no it isn't because it doesn't really work, being based on a false premise. Should one use feng shui principles in design even if they don't believe in it? That may be up to the individual, but it also may be like "playing" with a ouija board. Just because you know there is nothing to it doesn't mean that everyone has that same faith. It should be considered carefully, taking into consideration whether others would believe that you believe. In general, consulting a feng shui advisor, a palmist, or a medium implies a belief in what the Bible would class as idolatry.