Often with a scenario like this you must choose between using a PowerBI.com workspace or a Power BI Embedded workspace. However, if your requirements is to use dashboard tiles instead of reports, then Power BI Embedded is not an option because it does not support dashboards. Power BI Embedded only supports what you can add into a Power BI Desktop project which included datasets and reports.
If you are using workspaces in PowerBI.com, each user needs an Office 365 account (or more specifically an Azure AD user account inside an Azure AD tenent). Next, each user will require a Power BI licenses which could be either the Power BI Pro license or the Power BI free license. Note that while most Power BI users will have an Office 365 license, it is not an absolute requirement.
If the process of creating an Office 365/Azure AD user account for each user and configuring all these user accounts with Power BI licenses is impracticle or impossible, then Power BI embedded is the road to go down. It's just that you will have to embed reports into your custom web app as opposed to dashboard tiles.