What to upgrade first for better sound quality?

I would match phono stage to cartridge not the other way around. If I were you I would probably replace the Ortofon with Soundsmith Carmen or higher and see what happens. Then phono stage. Then speakers. Then amps. And cables.And power regenerator/conditioner.

Go with the herron and don't look back!

I suggest infrastructure.

First, clean up your records. I use 80 KHz ultrasonic cleaning, and it is like doubling the price of a major component (over my conventional record cleaner). Added benefit: extends stylus life. So before you spend big bucks on a wundercart, spend some money to protect it from groove grunge.

Second, clean up your power. Most power comes out of the wall looking like zombie apocalypse. Buy an isolation transformer from Plitron and put it in another room, because when it does its job it growls. For $1000 you get a significant sonic improvement (smoother) and, as above, protect your equipment from surges, DC, etc.