For the missing "b" segment on players 1, 2, and the master display, check R2 (10k) and see if it's cooked. If it is, swap it - if it still heats up and eventually burns, test with players 1 & 2 disconnected. If it no longer cooks, test them individually to see which display is causing the issue.
R2 looks ok in your picture, but worth checking. If it checks out, and the issues persist regardless of how many displays are installed, it may be an issue with IC9 (7180).
Steps for checking that chip from "Pin Repair" (using a logic probe):
"Check the input pins of the UDN7180A (pins 2,3,4,5,6,7,8) for pulsing activity. If there is no activity, either the master display board's connector is bad, or the input chips (4558) are bad.
Now test the UDN7180 output pins (pins 14,15,16,17,18,19,20) for pulsing activity. If there is input activity, but no output activity, then the 7180 is bad."
For the other issues:
From your picture, R12 looks like it's cooked; it controls the "e" segment for players 3 & 4.
R5 also looks somewhat cooked, and it controls the "e" segment for players 1, 2 & the master display.
Seems odd that both would be cooked, so definitely rule out a bad display as noted above - replace both R12 & R5, test with just the master. If neither heat up, and you have "e" active, then add the 1-4 displays back in one at a time, checking those resistors as you go.
If you isolate the issue to a particular display, make sure there are not shorts between pins; I found a display once where there was a short right where the signals went into the glass; scraping away some gunk restored the display to normal operation..
For the missing 100k digit on player 2 - probably a connection issue given how it appeared; reseat the same connectors you messed with previously, and make sure to re-seat J5 on the MPU board while you're at it.
If you've never pulled those (at least the MPU and driver) boards and reflowed the header pins, definitely check that worst-case.
Good luck!
Brent