How much memory for a MBP?
Since you are going to use 3 OSs- OSX Windows and Linux, I would say definitely, the 500GB sad drive and 16GB RAM. I use 2011 MBP with only the Mac OS and 8GB RAM as well as 500GB sad drive. Don't forget, anything can happen and have external storage. I didn't know that ssd drives had become available in 750GB.