As with most music software you would expect a smooth crossfade between songs wouldn’t you?
The transitions between songs so smooth even with songs that have sudden endings.
We currently use these settings for crossfading in RadioDJ
It's rare we have major silence between tracks
If we do ever hear silence it’s usually a cue point that hasn’t been set properly but that easily remedied using RadioDJ track/cue edits.
The fadeout duration has been set at 3900 for some time now and always seems to mix rather well.
If they are mp3 files you can use mp3gain to level them in bulk. It may take a few hours if your collection is huge.
You can also use Audacity to normalise the audio in tracks before you import them into RadioDJ.
Of course no settings are ever perfect from one PC to another you might want a longer crossfade duration but we find 3900 suffices for us.