Welcome to the community, and hope I can soon learn a lot from you
I don't know about the APA style, and about mediation analysis! But based on your post, it seems something like regression. If so, I can say those important parts for the model which should be reported are the F statistic, P, and adjusted R-squared. It is also good to report the difference in the adjusted R-squared values for each model compared with its previous model, if you have more than one model. Well the P and standardized coefficient are important for predictors.