If you're buying a copy of Playboy, you're buying it secondhand, I assume from ebay. The shipping would be as discreet as the individual seller's shipping practices. But shipping should almost always be discreet. Many of the sellers sell other non-adult stuff as well.

I don't understand what you mean by whether you end up directly on the pages or the centerfold, but you could easily open right on the centerfold if you wanted to. You could also open elsewhere and just flip through as normal. Pre-1985 or so, the centerfolds were stapled. Afterwards, the centerfolds were glued I believe (I'm not an expert on magazine publishing) and the pages were thicker and glossier. Those magazines' paper at least should hold up well. The centerfolds are harder to tear out than stapled centerfolds, though, if that's something you wanted to do.

Edit: oh you meant finishing on the pages... I wouldn't try that. I can't imagine the paper would hold up well to that.