Blacksmith upgrades, which ones and when?

I struggle in part because I'm not aggressive early on. I want to get my units upgraded before attacking. So a few questions on Blacksmith upgrades: Is there ever a game that makes it to imperial where you don't get all of them? Which makes the least sense? How many units should you have before getting an upgrade makes sense (instead of getting an extra unit with the cost of the upgrade)? Which upgrades first, offensive or defensive?