Firstly congratulations and my love and prayers are with you and your family. As a mother who had two close to each other, it was difficult during the pregnancy but just involve your son in everything you do, such as planning for the new arrivial. When your new bundle arrives make sure he helps out with little tasks like diaper changing (I dont mean leave him to do it himself!!) but just make it fun. Its amazing how close they will be - friendship wise.
They will be in the same class at school and go through the same changes etc. Also hand downs, so it costs less on clothing!! Most importantly...... ENJOY every moment of it. There is no right way to do anything, its just what you feel is right.
God bless you all