6']['9- I dunno, I clay (well, "spot-clay") with most every wash and it doesn't seem to strip my last step product or do anything else undesirable. I seem to pick up a lot of contaminants (yeah, I wash properly with a strong wash solution) and clay gets 'em off quickly and easily.
If you clay properly, it won't cause any trouble, and there's nothing wrong with waxing as much as you like (MANY Autopians wax every month). And claying before you wax WILL ensure you're not waxing over dirt. I say your brother is doing just fine.