You can use all the products on your neck as well. The most benefit comes from the daily sunscreen, then the retinoid in the PM. Ascorbic acid in the AM also helps to prevent wrinkles and even out the skin tone.
When starting the retinoid product, please go slowly: first using it 2-3 times a week, and slowly increasing the frequency to every other night and then every night over the course of 2 months to prevent irritation.
I'd recommend going for a simple but effective routine like this: https://whatsinmyjar.com/skincare-routines/public/4355
You can use all the products on your neck as well. The most benefit comes from the daily sunscreen, then the retinoid in the PM. Ascorbic acid in the AM also helps to prevent wrinkles and even out the skin tone.
When starting the retinoid product, please go slowly: first using it 2-3 times a week, and slowly increasing the frequency to every other night and then every night over the course of 2 months to prevent irritation.