A cost-of-living request is separate from a performance raise, and saying so protects your next merit increase. Reference published inflation figures for your country rather than personal expenses.
Yes. An unspecified request forces the other person to guess low or defer the decision. A figure gives them something concrete to take to budget.
Only if the recipient does not already have it in front of them — usually they do. The field is optional in this builder for that reason.
Ask what specifically would need to change, and by when. A documented answer turns a rejection into a plan with a review date.