I pulled up rpfm and did some tinkering myself to some of the values, and thought my experience with the changes might be useful to you. I changed it to 2000 background income like the other major factions and it did open up the game a lot more. I am not well versed in 3k, so the background income was raised for all minor factions and not just the huns, the effects of that to the larger map is unknown to me, since the Huns are sorrounded by major factions. I tried to see If I could upgrade the Huns from a minor to a major faction, but my limited knowledge made that impossible

I also changed the starting army count to 2, when I started having serious trouble breaking sieges in towns that had both an army plus a garrison. And 1 army limit doesn't seem to be a thing for any other faction. I have since changed it further to add extra army cap for each prestige level besides the ones you have already made.

I kind of started to be ok with the sacking bug letting only razing grant you infamy (It would mean you can't "game" the system by repeatedly sacking the same town), but instead I upped the infamy gains from the battle decision to an 8 and the razing infamy to 10 and 16 for minor and major cities respectively.

Finally I decreased the infamy decay for prestige level 4 and 5 to -4 and -6 respectively to off-set the lack of steady flow of infamy through repeated sacking.

I hope this was helpful, feel free to use any or none at all. Just wanted to share.