We are more likely to use "our chief concerns" rather than "chiefly". In fact, after reading some books on writing, use of adverbs like "chiefly" is discouraged as it adds little meaning to a sentence.
For your first sentence, I would use ' Above all ' : Above all, I wanted to know what he was up to.
For the third : I'll paint this wall mainly in red and that one in blue.
I'm not a teacher.
Student or Learner