I would not go with sandblasting but rather soda blasting. Sandblasting is much more aggressive and if the operator isn’t really good it can easily damage the hull. As to barrier coating, absolutely! Now is the time to do it if it does not have a barrier coat already. It is easy to do technically but can be hard on your back. Contact Interlux and find out how much epoxy barrier coat you need to use on your boat and then use at least that much. The number of coats is not the determining factor because my coat may be thicker or thinner than your coat, but rather the number of gallons of paint. Keep coating the hull until you use up the proper number of gallons. It is critical to recoat at the proper time or else you will have to sand in between coats. Then you apply the bottom paint at the proper time so you don’t have to sand before the bottom paint. I do my own bottom painting, it isn’t too hard except the crawling around part. Good luck.