Greetings - first, I use a funnel when pitching the yeast. The funnel forces the yeast to pour straight down and does not allow any to come in contact with the carboy opening. I typically soak my funnel in my 5 gallon bucket of StarSan solution a few minutes before use. No worries.
Second, I have read many reviews where the silicone bungs are very problematic. Drilling is an option, but rubber is the best solution.
I use a small piece of insulation to cover my temperature sensor and wrap a piece of elastic with Velcro strap around the fermenter to sample temperature from the outside surface. Seems to work fine.