If it can reassure you, i understand what you're meaning! And i like the design of your biceps hooks, very cool. I too ended up having troubles with SIMpixel's method and had to modify them to avoid breaking and improve the fit.
And about the masking fluid, this is indeed an excellent idea, i don't see any reason why it would harm the ABS and it works very well for protecting an area from paint. Same thing about the markers, unless you can't use them on metal i don't see why it wouldn't work. And as i can see, you already tested them on spare screws and it looks ok, so...