That's great not only can you participate in the challenges but also one of my favorite spots is the Critique Circle! The cool thing about that is you have to give critiques in order to receive them. I think it's one of the things that helped me want to comment on so many challenge articles. I want the feedback so I feel I should try to give as much back as I can.
It can be a little intimidating to enter the challenge the first time. I remember thinking I'd do an amazing job and felt a bit disappointed when I wasn't in the top right away. But it's worth all the worry beforehand and practice makes perfect.
The best advice I can give you is read some of the challenge entries now if you haven't already. The next is to hit that preview button before you hit submit. Give yourself time to let the piece set overnight then proof it again. Have someone read it aloud if you can, if not make sure you read it aloud a few times.
Congratulations on moving up to the Gold level. The benefits really are wonderful. Don't be afraid to ask any questions you might have