I joined a server last week which was full, not sure which race it was but there were two servers and both were full. It was my first time in what I class as a race and it was great fun. When I left the server I was 12th place with only 1min difference between 7th to 12th so I was happy with that. Think I was around 7mins behind 1st place though. As you've flown gliders you know the rules of the sky so just go join in the fun. If you get into a gaggle that helps too. That said I think there was a 3nm range for seeing other gliders set. It might be worth understanding about the final glide and how to use the GPS in the glider. That's one part I'm not experienced on at all, I know what a final glide is but I'm unsure on margins and what all the numbers on the instrument mean, something I must read up on. I scraped over the line though and still had enough energy to climb safely to turn and land. I did notice most were in the ASG29 however and I chose to fly the Ventus2CX for a change.
My real time experience so far is 48hours P1 plus my training hours which I can't recall, maybe around 40 to 45 hours. I've got my Bronze but still to fly my nav test (doing that this winter) so no cross country endorsement yet. I have my silver height and silver / gold duration. In short I am quite inexperienced and have never flown cross country for real though I do feel ready for it now so roll on next spring
I'd say don't be afraid to join any races. It's online, you can't break anything even if you do push a little too hard after all.