A middle aged fan! Ha! I see what you did there ;) It really subvert every expectation, didn't it? I'm glad to hear this sentiment coming from an older fan. For the costume change, I feel like he started to project only when he arrived on Crait. He never left Ahch-To, and he projected himself that way because he wanted to mess with Kylo Ren. It's the same look he had the last time they saw each other. Force ghosts are known to be able to phase with limited capacity, so I guess that's a blanket explanation for Yoda.