Mostly agree with TheDinge, would only point out that typically on any airline, availability of Biz class does not mean you will always be ensured an upgrade since they limit the Award seats irrespective of whether they still have seats available.

I only ever redeemed in QR once (though for 4 seats in one go), had no problems but would recommend that you do it directly over the phone (and in my experience, preferrably speak directly to a customer service rep in Qatar rather than locally in your country).

Happy travels!