Tonsai is alive and well, it is just now back in the jungle a bit. There are many different rumors about what is going to be built inside of the wall. Some people claim mega resort, others say simple bungalows. Either way, it doesn't seem to be happening fast. Still plenty of trash, but the beach front is actually fairly clean now.
I'm usually very prone to getting food poisoining (I got it twice in Indo shortly after leaving Thailand), but didn't have a problem in Tonsai (mostly eating at Mama's). That said, it's hit or miss, and I did see Mama washing the lettuce for the chicken sandwich under sink water, so steer clear of uncooked veggies. Load up on probiotics a few weeks before you go, and I would carry a supply of antibiotics.
I wouldn't recommend staying in Railay, it is super touristy these days and the vibe is a world apart from Tonsai. You're definitely less likely to get food poisoning over there (and there is some pretty good food), but it's not worth staying there in my opinion. Tonsai still is mostly climbers/backpackers, and is cheaper.
Koh Yao Noi (and Koh Phi Phi) climbing is good to go, except I'm not sure if access has been re-established to the grateful wall. Deep water soloing trips in general have stopped, except for Tonsai Basecamp's trip, but they won't take you to the best walls since it is illegal. You can still check out some of the stuff via kayak.
Feel free to shoot me a message if you're after more info.