Now here’s the kicker - you don’t have to pay again when you’re rebuilding tech 2. You’ve already paid for it. You have to spend the turn to rebuild and so you can’t use it this turn but if you had to spend the money again, you’d be really behind. So the turn was not that devastating for you thigh obviously losing a tech building isn’t fun and means you can’t have two heroes out, your base takes damage and any tech 2 cards in hand are dead cards for a turn.
It’s actually a very important distinction in Codex and in fact they used to joke that the name of the game should be Codex: heroes aren’t units. I recently played a game of MtG with my neighbor’s son (haven’t played it since the 90s) and there was a planeswalker card. I sssume you can’t target those with effects that target creatures, right? Think of heroes likes these then.
Lastly, Midori can’t be summoned again. He was killed last turn and so he has to wait a whole turn before he can come back.