On the community forum, there are games to play to win gold bars for each of the games. They are usually located in the off topic section and the new one is pinned to the top. There's also participation points and you can earn badges for your profile here on the forum. As far as cross promotions for the games, I haven't…
This is a known issue and they're working on it. Here's a thread about it here https://community.king.com/en/candy-crush-saga/discussion/257696/why-cant-i-send-or-receive-lives-help-on-candy-crush-saga#latest
Have you read the FAQ section? Here's a section with different topics on how to play. https://community.king.com/en/candy-crush-saga/categories/how-to-play-
Yes, that's me in second. I didn't get a screenshot of the ending of the race when I had over 43,000 color bombs. That was the hardest I ever had to play to win and got nothing but the I won pop up. This week I had 8,000 and won. I know you only get a prize for first. See only 2 minutes left.
Yes, the boosters are stored in the data of the mobile device. There's a topic in the ideas section of the forum for the boosters to be synced if you want to vote for it and hopefully it will be implemented.