I'm a new Starcraft 2 player, got it for Christmas, and Starcraft 1 was the last RTS game that I played with any regularity, about 10 years ago. I've played through most of the campaign on my friends computer, but got to the end and did not have all upgrades.
So is there a way to get all of the upgrades in the campaign? If not what are the recommended upgrades to get, and when. Also what upgrades should I balance with mercenaries? Should I save up for upgrades to things latter in the game or should I spend all my credits between every mission.