فاونديشن وبلاشر وبي بي كريم

No — pick based on the coverage a given day needs. Many people keep both and use whichever suits how much they want covered, rather than using both at once.

Yes, provided you apply enough of it — the tint doesn't reduce the SPF, but people often apply tinted formulas more thinly than a plain sunscreen, which does reduce protection. Apply generously.

Apply to slightly moisturised skin and blend with fingertips rather than a dry brush, building up gradually rather than applying one heavy layer.