As a modern "headless CMS", Sanity CMS is well-equipped to handle images. One of the most common questions I get from editors just getting into the Sanity Studio to work with their content is: "What size and format should I upload images in?". The answer is: "The bigger, the better".
The higher the resolution of your image, the better your possibilities for future use. For example, you may someday want to repurpose your content for print material, large displays, or redesign the website to use larger images.
Sanity's free plan includes 100GB of asset storage, which translates to 5,000 high-res 20MB images. If you need even more storage, each additional GB of storage costs $0.50/month per 1GB, available on the Growth plan at $15/seat/month.