There are some default expenses I'd like to adjust but I can't find where.

When you add a financed asset within the plan interface, a few default associated expenses like property taxes, maintenance, and insurance are nested within the same Asset form. You can use the form inputs to control how they are computed, or zero them out if they aren’t relevant or you’d prefer to model them as separate, top-level expense items where more customization is available (e.g. the Advanced change over time editor).