Can mediation be used to resolve all of our family law issues?

Yes. Mediation can be used to resolve all corollary issues stemming from your separation and/or divorce.
Decisions regarding custody and access, support and division of property can be mediated and then incorporated into a valid, binding and enforceable Separation Agreement.
The only issue that cannot be determined and resolved via mediation is divorce. The only institution empowered with the ability to dissolve a marriage and hand down an enforceable divorce order is the court.