Mischa is friends with Evgenia, she just called him and he was free. Even though David Wilson is based in Toronto, friends with Brian, and considered the de facto TCC choreographer, skaters are free to use other choreographers. He’s not really attached to TCC the same way Daniil is to Sambo. Choreographers are usually hired by skaters and not by coaches, though some coaches will make recommendations or have their favorites (ie Frank Carroll and Lori Nichol, the Chinese and Lori Nichol...)
It’s not common for choreographers to travel to competitions. Often their services are a “one and done” situation and the skaters and coach will change the choreo after they teach it (Shae Lynn Bourne talked about this in her TSL interview). Other times the skater will arrange for some choreo touch ups or retooling (Kaori did this recently with Benoit). David Wilson was sometimes in the k&c at Yuna’s request but iirc he was unable to get accreditation in Vancouver. Same with Rohene Ward at some events, but not major ones I don’t think. People have also misidentified Raf’s wife as Shae Lynn lol. I think the ISU is getting more relaxed with letting choreographers have accreditation but they generally do not get K&C privileges
Initial choreo is covered depending on the federation and the level of the athlete. I don’t know about the complexities of who paid for Tosca though. I believe Misha is coaching someone at Worlds, but he is also nominated to be on one of the ISU commissions. His accreditation badge says coach/choreographer. I am pretty sure showing up at practice was for moral support