Version actualized as of november 9, 2022.

Build with the main body of "D-Bot Core-XY 3D Printer" by spauda01
http://www.thingiverse.com/thing:1001065
with that very extensive and helpful documentation, which led me on this path,
some parts of "J-Bot Core-XY?" by JonnayLin
http://www.thingiverse.com/thing:1721957
and the "Beefed-up Corner for D-Bot / 20mm V-Slot Rails" by beepbeep
http://www.thingiverse.com/thing:1605514
I only lowered the upper front rail (N in manual) to just below the bed in Z-home position for better accessability of hot ends and bed surface (almost necessary with a 20x20 rail for the X-Carriage).

All moving parts went through a process of changes. These got their own thingiverse pages:
X - "X-Carriage, Linear, Modular, 20x20 V-Slot" by printingSome,
https://www.thingiverse.com/thing:3350550
This was changed a lot 0n 9 november 2022
Y - "Y-Carriage_for_20x20_X-Rail_Version-2" by printingSome
https://www.thingiverse.com/thing:4915787
Z - "D-Bot_Linear_Z-guide" by printingSome" (version with straight mounts)
https://www.thingiverse.com/thing:2779260
Z - "Back_Leadscrew_Bracket" by printingSome
https://www.thingiverse.com/thing:4246095
No need any more for the: "Z-Axis_Brake" by printingSome
https://www.thingiverse.com/thing:4245241
(see below).

Other parts:
Bed Support: "Bed_Support" by printingSome, https://www.thingiverse.com/thing:4916576
Electronics Box: the Rumba version of "SKR-V1.3, Ramps 1.4 and Rumba Enclosures for V-slot" by printingSome,
http://www.thingiverse.com/thing:2053035
"Ball_Foot for D-Bot by printingSome" dampens well with tennis balls, perhaps too swinging, not in use at the moment.
http://www.thingiverse.com/thing:2057063
"RepRapDiscount Full Graphic Smart Controller" by Trigubovich,
http://www.thingiverse.com/thing:1116163 for which I added some V-slot supports here.
3-point supported bed: "Präzisionsplatten - 326x326mm (Sparkcube XL) 3 Punkt" from filafarm.de, heated with a 300x300mm 220V silicone heated bed from China. I planned to use it with a PrintBite from Flex3Drive, but that was a waist of money, so now I am using Ikea mirrors 300x300mm and hairspray.

The wheels are completely gone, but I am back to the lead screw, I only use one at the back, after my adventures with the Bed Hoists.
The only problem with using 1 lead screw was the going down of the bed after power-off.
No more since I use one 8x4 lead screw in stead of the usual 8x8 one, despite the relatively heavy load of a 326x326x6mm etc.
I could not find a cheap one, so I used a Robotdigg "Tr8*4 400mm Leadscrew Threaded Linear Nema17" - part no. 17HS3001-400N84, which is a combination lead screw + motor.

One can buy a cheap but beautiful cover for the Solid State Relay, which covers all the isolated parts and leaves the hot spots open for the world to enjoy. ;-(
It seemed better for my health to make a less inviting cover.

The X-endstops you see go with the "X-Carriage, Linear, Modular, 20x20 V-Slot", the Z-endstops with the linear Z guide.

As for the electronics, I use drv8825 for the X- and Y axis with 1/32 microstepping and A4988 (1/16 microstepping) for the Z-axis. That last one was a great improvement when I still used the lead screws and wheels, and why not keeping it that way, although all my troubles with lifting the bed, with 2 or 3 lead screws and with 3 or 4 wheels, are gone. I now use the rumba, but that went well with with the Ramps1.4.
For the nimbles I use the A4988 as well (advice from the manufacturer).

Things I left behind in this process of changes, among others:
"Lead_Screw_Bracket (Self-Adjusting)" by printingSome
https://www.thingiverse.com/thing:2664656
which I still can wholeheartedly recommend for those using lead screws at the side.
X - "3-wheeled or Linear Railed Modular X-carriage (D-Bot Core_XY 3D Printer)" by
printingSome, https://www.thingiverse.com/thing:2206664
There is a 3-wheel version and a linear version and modules for the E3Dv6, the
Cyclops, the Chimera, with bowden tubes as well as with nimbles.
Z - "Bed Hoist for a 3D Printer - Final Version" by printingSome
https://www.thingiverse.com/thing:3732450

Edit 7 July 2021: remarks about another lead screw (8x4) and the superfluous Z-Brake.
Edit 24 July 2021: Y-Carriage_for_20x20_X-Rail_Version-2
Edit 25 July 2021: a new Bed_Support, some editing and image-changing.
Edit 9 November 2022: images changed according a renewed "X-Carriage, Linear, Modular, 20x20 V-Slot"