What file types are the best to upload for use in Portfolio when building my own site?

I cannot find any type of tutorial or support or file type suggestions when trying to build out my website using Portfolio. Will Portfolio be going away?

I am a graphic designer (primarily print based) who has build out a website using Portfolio. I already have done one, but want to edit it using a different template. I've started down that path, but when I upload images, the sizing is all over the place--either in a grid pattern or individually. How can I crop images so that it appears as a thumbnail first, but when clicked on or hovered over, it appears full size? And, what's more ideal to use: a PNG, JPG, and do I have to resize all of my images (prior, in Photoshop) to be consistent or can they be sized in Portfolio? Suggestions/feedback is appreciated!