I love to see what you're doing. And also a big fan of the roofing tiles, which I also use.
Something I've learned from 7+ years of using them for garden edging: They can break, and they can wash out if you have a place where water drains off.
My suggestion, if you're going to put them tallwise rather than lengthwise, is to find something to put them against - a plank, a pole, and then when you need to replace a broken one (after you trip over it, the dog bonks into it, you drop your shovel on it, etc) it's easy to stick a new one in. It helps even more if you have washout.
It is a devil of a job, and I say that having used an entire house's worth of tiles to edge all of my beds (not a huge space, i think my garden lot is 7m by 7m, i have maybe 9 separate small beds. it was many, many carloads of tiles, MANY spiders, many sore muscles. But totally worth it.) Godspeed!!!
Another idea for keeping brush down in your paths: if the tiles are like the ones we have here, they smash and crumble relatively well. (in fact often they are used for guerilla pothole filling when needed). So if you have a lot of them, consider running some over with a vehicle to crumble and put them in your path.