We recommend setting the site homepage to a general space that users will encounter when first entering the site–a default landing page replacing the Confluence Dashboard. See Atlassian's Configuring the Site Home Page for procedures.

Can users still access the Dashboard if we change the site homepage?

By default, no. Zen only includes a link to the Dashboard (from the Configuration menu) for admin users. To allow users to see this link, add the option in the brand settings:

Configuration > Brand Designer > Toolbar > Show Dashboard Link to Regular Users checkbox

Otherwise, use the Recently Updated and Space List macros to add Dashboard content to a page.