Macro Prompt for Input & Choices

I have been asked by my someone to make a macro in Word 2010 that will "highlight" user defined lines (example: every 4th line) using user defined colors (example: they can pick between 5 color choices but be required to use that one color for the entire document). I have created a very basic macro:

Sub Highlight()
Selection.HomeKey Unit:=wdStory
Do
Selection.HomeKey Unit:=wdLine
Selection.EndKey Unit:=wdLine, Extend:=wdExtend
Selection.Range.HighlightColorIndex = wdYellow
Selection.MoveDown wdLine, 3
Loop Until (Selection.End = ActiveDocument.Content.End - 1)
Selection.HomeKey Unit:=wdStory
End Sub

I would like to keep this structure, but somehow allow the "MoveDown wdLine" to be changed by the user in some sort of a prompt box as well as the "HighlightColorIndex" to be changed by the user. And, obviously I don't want them to have to go into VBA to make the changes.

Apparently they want to use this for some sort of a reading guide for large documents.

Any help would be appreciated.