♠ - What are they afraid of?
He is afraid of too many things, the twins could gladly tell you about this. Despite the drive of knowledge the man carries with him with every task he may take on, there will at least be one thing during the work period that will frighten him. Most of these fears come from the professor over thinking any detail that may lead to a bad outcome.
♦ - What is one thing about them that they are most proud of?
I guess his knowledge is what he is most proud of. It may have been his family at one point or another many years ago but I see that over time, when work became number one and when his wife left him, his priorities became a bit jagged. Thanks to Dipper and Mable however, I can see that maybe when McGucket was reintroduced to his forgotten memories that this may help him turn the tables.