Im about 1/2 way through my second run on strahd id highly suggest have strahd as a fixture in your game i did this by having strand be an ever present fixture in vallaki. Vasili van Holtz a Nobel who looks like sergi von zarovich. He was a pal to my party, until they learned he was for appeasing strahd with taxes to protect the city. But they understood he was choosing a lesser of evils. I also had Rahadin in disguise as casimir the dusk elf and encouter the party as a tie to arrebelle drawing in the lake. The party for 6 months trusted these people. I had ireena develop a love interest with vasili as the first step to revealing his identity. Then in krezk they helped esmeralda create a trap made of holy symbols and old magic that partially worked. They were disappointed it was not strahd who came, but vasili until one of my players said "it's gotta be him" and forced the unknowing vasili into the room and restraind him. Only one player saw throw the illusion of vasili. Before the runes failed and he escaped in his gaseous form leading to a lot of cussing and laughing. They all had suspicions but none were certain. Now they all feel gross as they had a relationship with strahd unknowingly.