A few questions:
1. ABC and XYZ are split, owing to many unresolved issues. What is/are the correct form/s to say?
a. difference of opinions
b. differences of opinions
c. differences in opinions.
2. What is the correct form?
a. high-spirited man
b. highly-spirited man
3. Is it formal to end email-requests with 'thanks in advance'?
I would use differences of opinion.
2 I'd use a
3 Thanks is seen as a less formal form.