If you want to try going with guides route, one easy way of making a fixed length guide is to start on the origin, then pull out on green and make it the length of your build plate. Now you easily see the cpoint but the tail is hard to see when it's on axis, so just move the guide off axis a bit for visibility. Now array 3 more copies. But since you can't inference to the tails, easier to array in a 2 x 2 grid that is sized to your build plate. Anyway, get the cpoints in place first any way you can, then rotate the tails in place later, just my opinion, there would be 50 ways of doing this. Then make them a group and move the corner back to the origin. Just a thought.

I'm late here, but anyway I am finding centers too a lot. But for me overall is quite quick to just use protractor tool. Left click on the midpoint of any segment, left click on one of the endpoints, pull out to perpendicular, left click again. Do this again for another segment, and you have the center. Rather fast overall.

TaffGoch.
Years and years ago, (eons, probably) this guy was the master at making geodesic domes in sketchup. Just using native tools. He used to be active on sketchup forums, but that was so long ago. I only find him now on a site called DeviantArt.

Got it

Ok. I only have free version of sketchup 2017 so I don't have Solid Tools that I know of. But I will look around. thanks

Nice, thanks. One question. It is when you came to the chamfers, after the "follow me" I was expecting to see an intersect with selection, then some tedious cleanup. But no, somehow you trimmed away that chamfered material all in one fell swoop. How on earth?