That looks like standard vinyl J-channel you can buy at just about any home improvement store. That's actually a great idea, I've never seen anybody use strips with that particular channel but it seems like it would be very easy to put up after everything is mounted to the channel.
OP, this would be my biggest suggestion. Make sure you get as much work done as possible before you get on a ladder. You could even get this J-channel, then attach aluminum channels such as these to the J-channel to make it easier to hang since the aluminum channel pieces are usually shorter than this vinyl J-channel. You could probably get two pieces of aluminum channel on each piece of vinyl J-channel. This is more work and money, but would allow you to use the aluminum channel with diffusers for extra protection and better light diffusion, and you could get the angled stuff if you wanted as well.
I'm not sure how high or difficult your rooflines are, but mine were bad. I had to rent a boom lift, so mounting little pieces of channel and then sticking LED strips to them after they were attached to the house was out of the question. I needed a more modular approach so I could put the LEDs up in smaller sections, but obviously I couldn't solder strips together on a lift with the strips on the soffit already. I went with Permatrack and pixel strings and soldered connectors on so each piece of track was modular.