Should I wait for the PLA to stop flowing out before printing?
No. If you wait until it stops, then by then there will be lots of air in the head and you will end up with underextrusion on the first layer. So not only do you not need to wait, you might want to "prime" it one more time if you do wait. The default start/end gcode in cura "primes" it a bit before printing. You may have taken that code out long ago for your ABS. Overall I think you will find PLA is easier to print due to it's reduced shrinkage when cooling.
When turning the gear wheel by hand, be sensitive to the amount of pressure that it's taking... slow down a little as the resistance builds, so that you aren't just storing up a lot of pressure in the print head, that will inevitably lead to oozing.
That said, some degree of oozing is pretty normal... just wipe the head off, and start printing. Once the print begins the pressure is going to build back up again anyway, so don't worry about it. It should still turn out ok.
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