Help with ECS scheduling and creating my own bevy plugin

[TirushOne]

So I am trying to get started with creating a prototype for a 3d sound propogation system for bevy, I outlined my ideas and theories for how that was going to work in this post #11322 (comment). But to get started testing my ideas I need to do a few things that I don't know how to do currentley.

1: I need to be able to run my code anytime ofter gameplay and phyisics updates, so during/after draw calls, but be able to block the gpu from update the frame on screen (even if it's done rendering) until my code is completed running. My understanding this that I can make my plugin register a system that will have a schedul attached to it that runs when I need it to, but the exact details of how I do this are unknowen to me.

2: during this pocess I need to be able to find all the entities that have the relivant components for sound propogation and read their data. I know this can be done through querying the ecs but I not sure if that is the best way to do it or not.

3: I need to add the componends that contain data needed for sound propogation but I don't know if this is something that should be done manually or if there is a way I can make the plugin automicley preporcess meshes into the meshes used for sound propogation, considering that the prepossesing is expensive and should only be done offline and not at run time.

Please provide code snippets in your answers if you can thanks. Any help is greatley appricated.