This contribution in Jan 2021 to help others along this path, as an experiment in transitioning from windows/ASCOM to the KSTARS/EKOS/INDI.

Overview
hardware configuration achieved was:
RaspberryPi3 - as master and noir Black and White
RaspberryPi2B - as camera - color ccd
OnStep Mount controller connected through USB
Focusers: probably go with the RaspiHatFocuser Driver (open item)


Step-by-Step - estimated time ( 2hours, including making 2 images)

1) Setting up the Pi3 Master: (60 mins)
1.1) download & flash latest build from astroberry.io (45mins)
1.2) edits required to turn off gpsd and restore USB0 for OnStep
Edited the /etc/default/gpsd script and made:
START_DEAMON="false"
USBAUTO="false"
1.3) config changes: change master password and enabled camera
1.4) change password for the astroberry wifi in wifi manager
1.5) optional, change password for VNC login
1.6) ran updates recommended on astroberry.io
sudo apt update && sudo apt upgrade && sudo apt dist-upgrade
1. restart

2) Setting up the Pi2B’s (if they´re really old, try this first) (60mins)
2.1) download & flash the latest 32bit image from raspberrpi.org
(tried ubuntu unsuccessfully)
2.2) configure wifi
2.3) change passwords
2.4) enable camera and ssh
2.5) turn on boot to CLI, turn off boot to desktop
2.6) install full indiserver and all libraries
2.7) connect to pi2 over ssh and test camera with
raspistill -o test.jpg
2. over ssh, start indiserver on raspi2b:
(at first with option -vv to see connections working, removed later)
indiserver -v indi_v4l2_ccd
*** session 1 on rpi2b ***
ssh pi@10.42.0.126
pwd: yourpwd
indiserver indi_v4l2_ccd


3) Setting up the Pi3 Indiserver through two terminal sessions ( 5 Mins or less)
3.1) Setup INDISERVER for FIFO mode, to be able to use identical camera drivers
***** fifo startup ****
indiserver -v indi_v4l2_ccd
***session 2 on rpi3 ****
mkfifo /tmp/myFIFO
indiserver -f /tmp/myFIFO

*** session 3 on rip3 ***

echo "start indi_v4l2_ccd -n \"bwpi\"" > /tmp/myFIFO
echo "start \"V4L2 CCD\"@10.42.0.126:7624 -n \"colorpi\"" > /tmp/myFIFO
echo "start indi_lx200_OnStep" > /tmp/myFIFO

3.2) have all of these commands in a text file on the raspi3 desktop, takes 30 secs to configure

4) Set EKOS to use locally running indiserver
4.1) Settings: (also, see image) !could NOT get webmanager to work!
Remote, localhost
No webmanager
Just picked each local driver: Onstep, V4L2 CCD,V4L2 CCD
Save and start EKOS Session - result worked.

5) Confirm everythings working
...by taking images with each camera, capture tab allows switching between cams

Helpful Sources
indilib.org/develop/developer-manual/92-indi-server.html
indilib.org/forum/embedded-indi/3580-fifo-start-script.html


Unresolved

Main intended configuration was: (because I had all of these lying about)
RaspberryPi3 - as master
RaspberryPi2B - as camera - noir Black and White
RaspberryPi2B - as camera - color ccd

I was unable to connect both Pi2B´s simultaneously - EKOS was always only able to launch one instance, although indi connected with both pi´s. Tried creating an alias through EKOS, which also didn´t seem to solve the problem
echo "start \"V4L2 CCD\"@10.42.0.126:7624 -n \"colorpi\"" > /tmp/myFIFO
echo "start \"V4L2 CCD\"@10.42.0.127:7624 -n \"bwpi\"" > /tmp/myFIFO

I was also unable to find the RPICamera driver in the EKOS menu, even after installing full indi

Clear Skies!

Chris