I am going to blow in additional celulose insulation in the attic of my 30 year old home. I only have about 10 vents in my soffet around the entire house. Should I put in proper vents at every other joist with the anticipation that some day I may reside the house and put new soffet on? Or, should I only put venting where the soffet vents are today and put the rest up if and when I install new soffet? Second question, is it ok to blow the insulation on some decking made of 3/4" board or should I remove all of this first?