Ah thanks for the detailed feedback. The images in the screenshot look anti-aliased. I've tested this in Unity and I'm certain these settings exist in Unreal too.
- #1 The image looks crisp if the image compression is set to 'none'. If there is a Resize Algorithm - set that too Bilinear or any thing lower for very clear art. If there is a Filter Mode - set that to 'Point' or 'No Filter'
Doing all these will make those images clean, and the UV lines will stick within it's defined area.
- #2 I'll consider a second pass on the texture to make the pattern more repeatable for the water.
- #3 - refer 1