Ok, here's my triangle pattern, after bringing artboard 1 into Photoshop and adding texture, plus making it into a pattern. I don't know why, but somehow my rectangle symbol on Artboard 1 got out of synch with the rectangle backgrounds on Artboard two, leaving me with slightly off triangles and lines between the background. Not sure how to fix that if you don't recognize the mistake right away. So I just worked with the basic tile in Photoshop.

Ok, I'm feeling more comfortable with the basics now. Made my own texture, drew a bunch of fish and used the vectorizer to add them to my second pattern. Added some little dots to fill in the base, and here it is: 

So yay, feeling a little less stupid and cranky, and I'm seeing where Affinity could be pretty useful! =)