Most maintenance / upgrades have been completed, so the site should be open to all, but all the new features have shown some bottlenecks that cause slow loading. We are sorry, we are working on it, and we will keep you informed!
I've been using MCCC since it came out, and I have never had an issue with save files related to MCCC. What does cause save file issues is having too many saves. As for how many saves, I couldn't say exactly, but I have experienced save corruption when I let the save folder grow to much beyond 5Gig. That's the only thing I've ever had problems with related to sims 4 saves.