URL parameters and automatic task assignment for online recruitment

URL of experiment: https://run.pavlovia.org/mlwell/stroop-demo/html

Description of the problem:
I am planning a stroop experiment using MTURK online recruitment platform (still cosidering Prolific over Mturk). My experiment will sequence of trials, each trial the will get a random pretreatment
My way to manage the sequence of trials users is through the qualification mechanism in MTurk
I plan to create a HIT in mturk that will send users to Pavlovia for the first time.
Tthe HIT will send to Pavlovia a parameter saying that this is the first time the user is in the system .
In my code i want to assign them to get the treatment or not based on some hash for their user-id.

Then i want to create another mturk HIT for the second time a user comes. Use qualification enable it only for users who completed the first HIT.
Again I need to create additional HITs for the 3rd, ,… rounds

The 2 main issues are:
1. I dont know how to send the parameter to pavlovia that tells it that this is the second round for the user such that it will know to send the user to the right treatment.

2.I dont exactly know how create the loops that will randomly assign workers to different pretreatment in the builder
I have read the Pavlovia and Blocks of trials and counterbalancing — PsychoPy v2020.2
but still would appreciate some guidance and tips on how to manage this operation

We aim to have 200 participant visiting at least twice so i really need it to be done automatically
Thank you