I really do like the increased barbarian elite limit. They definitely need that.

For the most part, I like this. But believe me, you do not want 6 cav allowed for civilized factions if you are a barbarian, that is a bad day. You want less than 5, probably 4 but 5 is good. 2 Heavies and 3 Medium-Lights. I think the cav rules definitely need to be revised since certain elite cavalry is under 3K. For example, Campanian Cav are like 2600 and are an cost effective counter agaisnt 4K Companions. I would spam these if I had the chance at 40K.

Cavalry should still be segregated with heavy/medium-light since the extremely powerful shock effects of heavy cav is the main issue. High end HA can't do that and neither can high end overhand spear cav.

Max 4 missiles is okay with the unrestricted skirm/light infantry that I've described earlier but you probably want a skirm limit somewhere since my Baktrian Light Infantry + Archer army can't be effectively countered by the barbarians except in trees.

The phalanx rules you have would be okay in theory but it makes phalangites too easy to counter by just running around and forcing the enemy to phalanx ball. An army couldn't just run past an enemy army to hit it from behind since it needed to guard its camp as well forcing a set piece battle. So I think the correct balance would be to make it so that phalangites can't be put back in phalanx once they are taken out of it in combat. I don't really have a problem with them being used for flanking running around since it strings them out and makes it easier to hit them from behind.

Steppe wise, I would say, max 10 missiles, max 14 cavalry, max 4 heavy cavalry. 6 Elites total. I usually use a 10 cav steppe army with a mass of cheap infantry. Steppe rules will be hard to make.

Also, Roman units with the discount don't really fit your infantry limit. You would probably categorize Triarii as elite despite the fact that they are really mediocre unless you want it that way.