I forgot to address the solder shorting out your power jack issue…
Are you sure that the pins of the power jack are shorted together by the solder? This would be very unlikely…the solder would solidify as soon as it hit the board, which would keep it from flowing under anything. I don’t know which pins you found connected, but 2 of the pin are supposed to be connected on the jack when nothing is plugged into it. Try plugging a power cable into the jack (DO NOT plug the other end into the wall yet…we don’t want power in the circuit yet) and then re-test continuity between all the pins on the power jack. Hopefully they are not connected anymore.
You should be able to peel off the solder drop that fell on the board without much problem. If not, send me some detailed, in-focus photos.
-Brach