Try having a timeline float that goes from 0 to 1, then multiply it by 360 and set it to the roll value.
As far as the rotation being off center, if you open your plane mesh asset, is it center on the origin as shown in the image? Or is it off from center?
If it is centered, I would take a look at the part of the timeline where you are actually moving the actor to the right. Instead of getting the right vector of the ship component, try the node Get Actor Right Vector
That does seem to work well. I wonder if just adding to the current relative rotation was the thing causing that weird leftover rotation, which, now that I think about it, isn’t really needed. I think that idea was left over from one of my many previous attempts, haha.
As for the pivot thing, I double checked my mesh, and it’s exactly centered where the x and y/red and green lines intersect, and when I hit ‘show pivot,’ it’s right where it should be.
I wonder if it has something to do with my strafe location displacement?
Well I’m glad the rotation is working! Did you see my last post about the Get Actor Right Vector?
Oh, no I didn’t, my bad. I’ll try that now.
Thanks so much for all your help, by the way! I really appreciate it. I’ve been fiddling with this problem for weeks.
Ahhh, it works! I’m so happy! Haha, I was so stuck on that problem for so long!
Now all it needs is some polishing, I think. 
Thanks again for all your help!
No problem! Just glad I could help. PM me if you run into any other issues!
