Can there's be individual levels? I usually run those most of all because of time

Those are called time trials and there's separate pages for those. If you're talking about quick runs or whatever they're called, seems questionable. Still basically just a time trial but with a little item RNG.

Mostly time trails but quick races would be cool too

Time Trial leaderboards are on the Players' Page: http://www.mariokart64.com/mksc/.

Thx