sanding was pretty easy just used a 3" palm sander and you go up and down till you see the black lines between the steps disappear and rotate it slightly, i was really surprised by how little time it took. Brought it down with 120 then went to 400 then to 600 grit till it felt soapy smooth.
Yup slight friction fit just to the point that it wont come off if you shake it around hard. You can easily slide it apart with just your thumb while holding the handle. Was considering magnets but felt like that might be cheating a bit heh, that and im running low on magnets need to restock.
As for the plywood its the same stuff i use for about 90% of the things i do. its 1/4" plywood with maple veneer on one side and it is pre finished on that one side. it says 1/4" but it averages between 0.188 to 0.205 depending on the sheet but remains pretty consistent across the whole 4’x8’. I don’t use proofgrade as shipping to my address is insane.