One upgrade to business class is already going to be a few hundred dollars. 10 exceeds it by a wide margin.
20%? What airline you're with, for "elite" statuses it's generally less than 20% of the flights that do not get upgraded. Obviously depends on availability on the specific flights though.
On a long haul international flight ? I doubt it. It's hard to find even mile redemption availability.
Depends on what you fly. I always used to fly first flight out of Newark preferentially compared to anything else out of Newark/LGA/JFK simply because I always got upgraded without fail. First flight out of Newark leaves before the mass transit gets running. So you can game the system to make sure there are seats to be upgraded to.