Glad to hear you had fun with the game : )
And to answer your question:
1 & 2. You're right on that assumption, it only can be gotten after finsihing that quest. There are actually two coins in the mermaid city. There is a hole you can enter with mouse form. You probably missing that I assume.
3. I assume you accepted the request at the guild but she isn't there, that would be quite odd. I think I did found the problem, will fix that in the next patch, thanks!
4. Yes but it is pretty much impossible to find. It is in the volcano behind one of the stone pillars^^"
5. After you have unlocked a certain transformation you can go back into that high tech place, in there you can find a sparkling spot on one of the machines.
6. Yes but only in ng+, there you can get both. In the first playthorugh you only can get one.
7. Yes, there is a card collection app, you get it in the casino.
As for bugs:
1 & 2 & 3. Thanks will fix that! And good to know, will also fix that. And also will take care of them!
Feel free to me if you should encounter more bugs or have feedback!