To reset the counter you have to use the Reset Counter behavior, and it make the counter value to 0.

By using a counter. So if you want only 10 correct answers then every correct answer will add 1 to a counter. When the counter value hits 10 then the game ends.

You can use the swap behavior to change a text element with another text element by swaping positions.

If I understood I think you can so this with Shuffle random group. So one group will be the objects, and one group will be the text elements. You will need two shuffle random group behavior invoked on page load for both of groups. If you have for example 10 words, you can leave only one of them on screen and place the other ones outside the screen. So you never know which word will be displayed on screen. Every object will have three behaviors: Hide self, Hide the text and two shuffle random group so it will shuffle the objects/text elements again.

And this way you can do with the questions to: leave only 10 of them inside the screen and the rest of 490 outside the screen. All the questions will be in the same group so when it will shuffle randomly you will never know which questions will apear on the screen.

There is no special feature on how to select a specific element from the group. Could you give us in more details what  you want to do so we can find a way to do it?

The house element should close the app so you probably saw the "You chosed to close the app" message.

You have to hit the subscribe button on top of the page in the Notification area:

First chain the Counter Display to the Counter Set and leave only the counter set to Execute on Page Load.
Secondly chain to the Counter Add a Counter display also, so when you add to that counter it's value will be updated

I've attached a sample app to see how to display the counter on Page Load. Also if you tap the +1 element, the counter value will increment with 1:
100 - counter display.zip