What is the ideal sizing for the feature image for it to look right on the home page and the slider? or the ratio it needs to be
Please try to keep all images under Full HD (1920×1080px) and under 1MB.
WordPress automatically generates three more image sizes (Thumbnail, Medium, and Large), so you don’t have to upload different sizes.
Hope it helps, but if not, please ask any additional questions.
Kind Regards, Roman.