I've tried looking up on USFSA web site to get some guidelines on how juvenile or intermediate skaters qualify for jr. nationals, but I didn't have any luck. Is it based on more than top finish in qualifying Regionals or is also based on that combined with competition wins?

It's Regionals only, except for pairs & dance, which go directly to JN--they no longer have to qualify.

Pairs and dance teams have to qualify at Sectionals. There was a direct advancement to JN a few years ago, but only for 1 year until they made provisions for the events at Sectionals. I think it's the top 8 at each Sectional that advance.

__________________
Terri C is a Bronze lady!
Gold Moves, here I come!

It's based on the total population at a level in qualifying and the number of skaters in your Region. More populous regions get more "spots" but the min number is 4 per Region.