SQL practice: Reading a Query Plan: Indexes That Earn Their Keep

Create an index named idx_orders_order_date on the orders table over order_date.

Create a partial index named idx_orders_pending on orders over order_date, covering only rows whose status is 'Pending'.

Create a composite index named idx_order_items_order_product on order_items over order_id and product_id, in that order.

Create an expression index named idx_customers_lower_city on customers over lower(city), so that case-insensitive city lookups can use an index.

Create a unique index named idx_products_name_unique on products over product_name.

EXPLAIN ANALYZE shows a Seq Scan on a 50-row table. Is that a problem?

EXPLAIN ANALYZE reports rows=12 estimated but rows=480000 actual on one node. What does that most likely mean?