I plan on building in the case for all the correct lengths, then flushing and filling the loop outside using a USB to fan adapter to power the loop so I can shake the res to get any bubbles out before reinstalling properly.
Parts list looks good, although like @PBJ suggested, either a quick disconnect and reservoir or a T-fitting will help you immensely in filling the loop.
Also don't count on filling the loop outside the case and then being able to get it all in the case. AIOs do this because it's just 2 components. But with a custom loop it's not possible unless you explicitly plan your loop for that purpose. You're probably gonna end up with lots of longer than necessary tubing runs...just build and fill the loop in situ.