Is there any way to make next:
1. have fixed thumbnail sizes with uncropped images? (for example 150×150, scaled, uncropped image)
2. have fixed size of main gallery image container? In case we have “tall” picture, it will be contained within some fixed size.
1. You would have to upload an image that is that size already. If not that size, it would need to be perfectly square and sized down with CSS. So if your image is 300×300, you can size it down to 150×150 with CSS.
2. Not too sure what you mean here – do you have any examples?