Only main body requires supports, the best way it to use custom support plugin for cura, only mounting points for RPI require these custom support, you can play with angle settings to try and build support automatically only for those.
For connections it's all snap joints except RPI to Screen screws, 2 M4 to make swivel connection to 2020 mount and 3 M4 with 2020 nuts to connect everything to the printer.
To make good snap joints make sure your printer is calibrated, if you have troubles with connecting the pieces, read about "horizontal expansion" setting in cura. Play with it to make parts snap nicely.
Total print time for all parts on my Creality Ender 5 Plus took about 8 hours.
1. Print 4 things (don't print enclosure.sql with everything, this is only for display/3D model on thingiverse) Front cover, back cover, main body and 2020 mount.
2. Put screen into front cover, making sure the thicker border goes into the part without pads.
3. Connect DSI cable to the screen, bend it a little so it will make 180 turn at least 2mm from the screen's PCB end.
4. Snap main body to front cover, fixing the screen inside. Make sure you clean up mounting holes for RPI
5. insert SD card into RPI, test everything
6. put RPI into main body, screw it in with 5-6mm long screws to the mounts on the sctreen through the mounting holes in main body. Make sure DSI cable goesover RPI, in front of SD card.
7. Make sure back cover inserts are not over-extruded, file the side of the back cover inserts if they do not fit in main body slots (It should fit if you set your horisontal expansion setting correctly and your printer is not over-extruding)
8. connect DSI cable to RPI
9. Route RPI camera cable through the hole in back cover (if you want to connect camera)
10. Snap back cover on main body.
11. Using three 2020 slotted nuts and m4 bolts connect 2020 mount to your printer frame (alternatively you can screw it to your table or anywhere you want to put RPI permanently, the mount has flat bottom, so it can be mounted on any flat surface with appropriate fasteners)
11. Using two 12-14mm M4 bolts and nuts connect body to 2020 mount, setting desired angle.
You have a choice of mounting flush with 2020 frame, or with offset, bending inside or outside of the printer, and you can mount it either on the horizontal 2020 (for portrait orientation) or on vertical 2020 (for landscape)
Before you mount everything permanently, make sure you follow OctoPi TouchUI instructions about screen and touch interface orientation.