Nothing looks out of the ordinary with switches.
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Ok, so check the diodes on all three trough switches, outhole switch and both saucer switches.

When you go to solenoid test mode, do they activate in correct order as per the manual?

Switch matrix issues manifest themselves when more than one switch is held closed (i.e. like a stuck switch/shorted capacitor on a switch, a fallen drop target or balls sitting in troughs/saucers - likely your case). Unfortunately the Bally switch test doesn't report all switches it senses as closed, only reports the lowest closed numbered switch.
So in switch test mode and with all three balls sitting in the trough you should be seeing switch 28 reported as closed, if you now activate all switches from 25 downwards one at a time, do any switches report the wrong number?

Report your findings to number 6. above.

This is normal. So long as there's credits, hitting the start button any time on the first ball will add players. Once the game has reached ball 2 or higher, pressing the start button will cancel the current game and start a new game at Player 1.

Good find!

Be careful. Gold plated switch contacts shouldn't be cleaned with anything abrasive as they'll decline from there on with poor contact. To clean them, just swipe a business card between the contacts while holding the switch closed. Use Isopropyl if you want.
Abrasive cleaning should only be used on tungsten contact switches which carry high current. These contacts are silver colored and larger in size - usually found on flipper cabinet and EOS switches of that era game.