Hey insight, you questions are very reasonable for a Christian to ask. The one thing I keep in mind is that this world was created by God...everything is His. The devil may try to take claim to things that do not belong to him but we only give him power when we fear his power over God's.
Yes, there are some grey areas in natural healing that Christians should not conform to but always remember that even though things like yoga, karate, herbs, meditation and such may have some negative elements that are attached to them it does not mean that the whole part is evil. Satan is the master of half truths. He takes the truth and attaches his lie. Take back what is not his and claim the part that is true.