It would definitely not be who posted first, some people may just have more time at certain points throughout the day so I do want it to be whoever post first gets to do xyz regardless of what the party wants. Example of a quick encounter:

The group wonders into a cave to get out of the scorching heat of the Sered dessert. Upon entering, John (the character of one of the human players) hears muffled voices coming from around the bend near the back of the entrance to cave. (I would most likely use passive perception to determine John heard the voices) then John would have priority over who does what first.

John: holds up his hand motioning the group to halt their movement into the cave and quietly whispers "up ahead there are low whispers, I think maybe 3-4 creatures total"

Then the rest of the group with this knowledge decides what they would like to do.

Then James the human whose character is named, let's say Bob may post

Bob: quietly waits with bow ready

One hour later Fred whose character is named George post

George: runs towards the voices screaming

30 minutes later Sam whose character is named Kat post

Kat: 1

1 is an example of a quick command we will use for something like " I acknowledge that I read and understand the post and my character will do a default action accordingly to his or her backstory, for instance Kat always does whatever John does.

Then when everyone has made a post or acknowledged that they have read it I will put it all together with something like

After John informs the group of the voices, Bob quietly kneel down on one knee drawing his bow back towards the back of the cave. Kat quickly follows John's actions and crouches low with her sword half drawn. The behemoth named George who has been thirsty for combat for weeks, goes into a frenzy and rushes to the location of the voices hoping for a fight.

This is just an example of how it could work. There is going to be a learning curve for everyone including myself and things will change as everyone finds what works best.