1.) The high pitch sound is ultra sonic frequencies, the general idea is to lower them, in fact, if you play your system audio high enough, you should be able to audibly hear them.
2.) I’ve been told by other creators that silent subs work better without extra sounds. Just the converted affirmations are optimal.
3.) Depends on what formula you want, but I’d listen to the tracks before converting them, then convert them if they sound good before that.