The easiest would be to use 1 RPi for every screen to ensure scalability, and wired network connections between the nodes to avoid delays and dropouts. Configurations with multiple displays per node will be substantially more tricky to set up and operate.
I think the cheapest configuration would be 4 x RPi Zero ($5 a piece) with USB network adapters (less ...
I had the exact same problem.
Turn on the screen first. I give it 4 seconds. Slower SD cards won't have this problem, since the Pi waits longer before checking for a monitor.
Add/uncomment hdmi_force_hotplug=1 in /boot/config.txt.
Turn off OpenGL. sudo raspi-config --> Advanced Options --> GL Driver --> G1 Legacy.
Get a HDMI screen.