Congratulations on finding Harmony resilient to errors and random draws (paraphrasing your comment of difficulty to draw a bad hand). At higher ranks, and prorank the story is different. While the deck is quite consistent there due to the harmony tag, draws and tactical gameplan per round become...
Regarding the first question: yes, you will unlock everything in the Geralt journey un to your current level, and if you have completed quests in Geralt´s journey, your will get also those crowns.
Not sure about the 2nd question.
A small correction, I think they are not even cards. Or at least count as a card, I used once The Great Oak to kill an enemy, a stratagem was in the row ... and lol & behold, it did one less damage!!
I think the underlying issue with stratagems is to find a proper synergy with the played deck (in case of blue coin). This point goes in hand with two views:
1. Stratagems are thought just as an extra card.
2. Stratagems are thought that have to be used on the 1st turn.
An unaddressed point is...