Short answer
HubSpot's KB: board cards can hold up to 15 display items in total, such as properties, associations and other sections. Board settings and card contents can be set account-wide or personally. An approvals section on cards needs Sales Hub Enterprise.
1. The board
Deal board in my demo portal, with card tags and stage totals.

2. What to show
- Amount and close date.
- Next step or last activity.
- A tag for stale or overdue deals.