Yes you are correct

U need to make the gemstones ( underwater bench) and repair additional items

To transform into the highly desire, highly used, green stones

Yes.. Use them on the bench n it will increase your ranking (stars)

The link appears to be broken

Can anyone tell me how to send sea horses after bricks??

I was wondering about the sea horse collecting bricks also. Have you figured it out, or has another player responded? In answering the second part of your question, The ice star, and coral, were in previous events. They will reappear but may take a few months until they run the event again (if they choose too). Hope it helped.