Power analysis for moderated mediation (and a small research design question)

#1
Hello guys! I am doing research on the effect of a specific medicine, quantified by dosage, on specific feelings (to be called; SF), mediated by feelings of connectedness, in which the relationship between the medicine and SF (X - Y) ánd the relationship between medicine and connectedness (X - M) is moderated by time (W), quantified as a number of days. To my understanding, in Hayes PROCESS, this is model 8 (see image).

I would like a power of .8. With an effect size of r = .20 - .30, I was wondering how many participants I would need to show a correlation between the variables if there is one (alpha = .05). I understood Monte Carlo simulations were a good idea for this. I found a website app that used them, however, it did not support this model.
Does anyone have an idea on how to best approach this, or is someone able to help me out with the power analysis? Thank you so much!

As a bonus question, I was wondering if there was a better way of quantifying X. Right now, the variable "medicine use" is quantified as grams of usage, which can be between 0 and 30, in which 0 equals no use. But this is not really a continuous variable. There was the idea of just making four groups: no use; little use; moderate use; large use.
model8.png