What's the best image size for a Blog in Minimal and can I put products into a Blog post?

What’s the best image size for the featured image in a blog please? And if I want to add more images in the blog can they be different sizes, or will that leave a lot of white space to the side of it? Ideally I’d like to feature products in the Blog, that’s what I’m writing about eg. new school shoes styles for this year. I’m assuming I can add a hyperlink to a photo that links the photo to the product, but wondering if there’s a way to just “add” that product as I would if I were writing a marketing email in Mailerlite that is synchronised with Shopify.