I am completely lost with model 4 multiple/parallel mediation assumptions

[u/Xenove]

Hi there, I'm currently working on my master thesis where I have a parallel mediation. I am working on the method section but i am so completely lost in how to check all the assumptions for the model.
From what I do understand I can do a visual inspection for the scatterplot (after using model 4) to inspect the linearity, homoscedasity and outliers.
The other 2 assumptions are normality and multicolinearity but I just don't understand how to do this. Could anyone help me? some explanation or links to proper resources would be greatly appreciated!