First off, you should be using a plastic scraper. All of the plastic scrapers I have ever seen have been make out of polyethylene (I have one that I suspect might be polypropylene, but I don't have access to a GC anymore to check). HDPE has limits on its maximum hardness, meaning that it should be very difficult to scrape your board hard enough to damage to the base (without also wrecking your scraper simultaneously).
Waxing is half art, half science. Since karasene is fast becoming a wikipedia enthusiast, this entry should tell you most of what you need to know
Ski wax - Wikipedia, the free encyclopedia