When a lower case i is used, this means to play a minor tonic chord. Any of these chords can be fragmented down to a R5. All of these progressions are triadic, yet can be extended to 7, 9, 11, & 13 type chords.
For a given Roman numeral, play either 3 or 4 beats. You can also extend the number of measures (or beats) to any number. Try different strumming patterns.