Idk, I bought my roll of the 3m stuff from AAP for like $22. Wasn't worried about price but I am not sure how the 1/4 will work. The 3/8 fills the channel perfectly and none squeezes out when you press the lens in. The 1/4 might not be enough. You do not want water getting in, so don't let saving $9 cause you to redo the project!
The relay harness is H13 yes, it just plugs into your oem harness and it's good to go. I wouldn't go above 5000k you will love the lights compared to halogens. It's crazy!
Halogen high beam
4300k high beam
Just a slight difference LOL.
A lot of people come into AAP where I work and try to get better lights and bitch about $30-60 for brighter sylvania bulbs. I explain to them how I spent $270 on a projector retrofit and another $275 on two more headlights. That usually shuts them up!