overlapping audio on separate tracks with individual fades in and out. Is there a better way, though? Any fan edit-specific techniques on trimming out extraneous lines/scenes? I searched YT, but there doesn't seem to be much in the way of fan edit-specific tips.
That's pretty much it, there's no magic bullet. Sometimes stuff lines up right and sometimes it doesn't, especially in stereo. You can try to get into the wide worlds of EQ, noise reduction, AI assisted track separation, pitch shifting, and other manipulation and repair tools. Nothing's perfect, exactly, but some can help. Some beginner tips:
1. Test out the different fade "shapes". There's linear, ease, and likely some others. Often linear is the default but I find easing to be a better choice in most cases. I'm not sure about Vegas, it may even let you edit the easing curve manually.
2. If you can, try to go for surround sound. Even with bleed through into the center channel, it's so much easier to edit, and to hide cuts, than stereo. Gives you more options basically.
3. Make sure if you're cutting out a portion of music, you're maintaining the beat as exactly as possible, zoom in to the track for granular control. Being zoomed out most programs will try to snap to arbitrary places in the timeline unless you turn that off, but it's still less control even with that off than if you zoom in.
4. Also with music try to make sure the new transition makes musical sense, but that might be a matter of luck or a matter of cutting slightly more or less to make it sound right with what's available, might not work exactly according to the initial plan, be prepared to improvise.
5. In some cases adding heavy reverb that lasts past the fade on the fading out part can help blend it with the fading in part