Oki dokies. A couple of things my little Hestern.

I have a feeling you will face difficulties because
1. requiring people to turn off ui is not practical.
2. requiring them to lvl/make gil to buy gear to attempt to blend in.
3. if you were to have a large turn out, there would be an issue of everyone being able to see each other to even seek them in the first place.
4. keeping track of an activity like this with a lot of people will prove rather chaotic

vs. last weeks lalafell march event. 'show up' 'follow me' '???' 'profit' ...there was a lot of ??? XD

Now I understand what you are trying to do, because I have hosted similar events in XI and XIV... but I had a great tool as a marker in the LS. For example if you were 'it' you just turned off your LS pearl symbol. Easy as pie! But you no longer have this convenience.

I would make recommendations to you.
'Naked race' (either by survival in aggro mob areas or through towns)
'Heckle mob' (You say in LS chat 'poke Yoshi P!' then the mob surrounds the player and /poke emotions them for about 30 seconds before you pick a new target and new emote)
'Beach party' (Show up in Costa Del Sol for screenshots and frolicking fun)

These are things I considered doing myself... but you posted first XD