Hey.. I may not be the best person to advise on this, but I ran into similar "thoughts" in my build. . First, I would def load the sumps from the sides. I think removing the side panels may be easier to do then the "struts", they don't look like they are bearing any weight but double check on it.. put them back on with hinges. . If you want to "play" with it later. ....
Here is what I wished I had done different on my. ..I may do it next time, if ever I need to empty out the sump. I wish I had built a Dollie to support the sump. That would lock in place but also roll out pushing the sump out from underneath the tank (needless to say after the drain and return line are disconnected. Maybe just a foot or so.. in my case I have 42" of stand hight to play around in there. But in a shorter stand that may be very very useful. Just a wild idea.. I had when I realised I will need to dump the mud in my rear refugium chamber.
The skimmer. The clear tube in the picture seems to be what needs to connect to a pump, or be fed from your over flow. . In My case I "T "off the return line with a valve in case I run one of those, or reactors, or uv.. or all of the above later. ..