At sign up, there will be two different groups
Group 1 will be for black, red, yellow, white and matching Disney-ish papers.
You pick 2 open letters. (At this point I am assuming that we will not have 26 swappers to make a complete alphabet, but 13 swappers means 2 letters per person). So say you pick E and S. You will make 13 sets for the letter E and 13 sets for the letter S. The set includes one 4" letter and a matching mat, box and element. So you make 13 letter E, 13 mats, 13 boxes and 13 other element (maybe a file folder or tags, or slide mounts etc) Then you make 13 letter S, 13 matx, boxes, and 1 element. In return you will receive the letter A with its matching mat box and element that someone else made, the letter B with mat, box, element that someone else made etc....
Group 2 will be theme specific. Again, at this point, based on expressed interest, I am assuming we will be going with 13 swappers which means yous will need to pick 2 open letters and state your topic. Let's say you pick A for Ariel and T for Tomorrowland. (I think I would like to stick with nouns -- so words like Believe and Arrival are out) You will make 13 sets of each. So you will make a 4" A that is embellished for Ariel, and a matching mat,box, 1 element (could be a paper piecing, a quote, tags, etc) You will also make 13 sets of the letter T - -4" T embellished like Tomorrowland, matching mat, box and 1 element.
The 4" letter -- yes, just set your cricut to 4". You will notice that some fonts won't give you a 4 inch letter, but don't worry - -it doesn't have to be all that precise.
Does this answer everything? Please let me know if it doesn't.