I'm putting together a nine-track vinyl compilation from various artists and genres. The tracks all tend to be pretty well recorded but the levels are somewhat sporadic. I'd like to get all the tracks into a somewhat consistent zone but I'm not sure if there's a definitive method for doing so.

I have the tracks in AIFF format, and I have access to various audio programs: Digital Performer, Audacity, Sound Studio, Garageband.

Mainly I am wondering if there's a simple system for adjusting the levels and being somewhat assured that they're more or less consistent, perhaps something more scientific than just trusting my ears, and then locking that in place.

A secondary question is if anyone has advice on applying any effects or plugins or "warmers"/compressors etc now that the songs are all finalized? Things I should/should NOT consider?

This is all something of an experiment, I'm not set on being the mixmaster for certain, but I'd like to play around and learn and see how things work. Your help getting me to a starting point is very much appreciated.