Elopements are meant to be small in numbers, preferably just the couple . There is no magic number for this but think under 10 people total including vendors. Anything over that and under 25 is considered a small wedding. If you are having over 10 people be a part of the day , make sure you secure a location that can either be reserved or obtain a permit to hold that many people.  Colorado has a lot of options for outdoor feel elopement-type events. Some outdoor areas can accommodate guests with proper permitting!