Type of Analysis and G Power

#1
Hello, What would be the best analysis to use to determine the relationship between parental support and mental health outcomes in later life among gay, lesbian and bisexual people? I plan to one assessment that determines stage of sexual identity development, one that measures parental support, one that measures trauma (covariate), one for depression, one for anxiety, and one for substance abuse.

Once that is done, what do I plug in to a G Power Analysis to determine a necessary sample size? I downloaded the G Power 3.1.9.2