Only moisturizing when hands feel dry and, most importantly, completely neglecting daily sunscreen application on the backs of the hands.
You can, especially leftover serum or retinol on your hands after applying to your face. However, dedicated, richer body products are often more cost-effective for larger areas.
Yes. Extending leftover serum (like Vitamin C or retinoids) and moisturizer from your face to your hands is an effective way to deliver potent ingredients to this area without waste.
You may need to treat different zones differently. Use a balanced cleanser, and consider applying a lighter moisturizer on the T-zone and a richer one on the cheeks. A niacinamide serum can benefit the entire face.