SO3 Assembly tips from a beginner.
First everything is heavy. Heavy is good! From the box at 55 pounds, to all the parts. Even the provided sharpie is big.
Find a sturdy table at a good working height with lots of light. This will save your eyes and back.
To separate the nuts and bolts into correct sizes, some form of a quick measurement tool is required. I used a Harbor Freight digital caliper. It measures in inches and in millimeters. There's a bunch of oddly sized standoffs. The digital caliper was critical in getting the correct ones.
Get a few, I used less than 6, small bags to separate parts. Separating the m5x16mm from the m5x20mm into their own bags not only reduced mistakes, but it really sped up the assembly process.
The wasteboard is made of MDF. Both water and oil are bad for MDF. A couple coats of polyurethane will seal the MDF. Quick light wipe with high grit sandpaper, 300 to 600, will smooth out the poly after each coat. Do this a few days before assembling the base. Poly takes about a week to fully cure.
The big extrusions, as said before, are heavy. Be careful handling them. The cut ends can be quite sharp. Yep, the cut on my left thumb proves this point. One of the three extrusions was full of chips and those chips can be nasty as well.
As every teacher you ever had said, "Read all the instructions before you begin."
Shapeoko 3 - #13, dust deputy, precision collets, limit switches.