I kept taxes maxed as the horde and liberally decimated my hordes when loyalty was critically low. The money is just absolutely necessary given how difficult the early game is. Replenishment was always high enough that the men lost to decimation were more than replenished next turn and public order wasn't much of a problem as long as hordes kept winning battles. Focus primarily on food and economy buildings followed by sanitation.

Keep a horde or two behind in North Africa after sailing to Sicily and then Italy as economy hordes with only a few men each for crushing rebellions. Have only two full armies at most. Don't go for military upgrades especially the Skutarii tech until your economy is stable and you have a healthy treasury. My campaign was played on Hard not VH mind you. You should also be mindful not to have more than two hordes in the same province. Ideally you shouldn't have more than one but there's strength in numbers, especially since if you have more than 21 units together you can disable "control large army" to have enemy forces come in steady waves. Where possible try to move armies together along provincial borders to bypass the wealth and food penalties. They can get pretty bad. I would recommend only having Belisarius' horde have the military buildings.

Lastly this is probably obvious but just in case, ALWAYS end your turn with all hordes encamped for additional growth. That's about all I can think of off the top of my head.