Haven tactics.

Back in the day, I used to max out Humans to the limit, experimenting with them every which way; the problem was Dwarves and Necromancer-mages—I won about 6-7 out of 9 games. I lost to Undead with the ult.

Mini-guide based on my own experience (Games Vs 2-3x human vs AI)

I'll describe the builds that carried:
I almost always take Dugal since he gives a lot of archers right away (fast farming). I build the tavern and look for Axel; if he's not there, no big deal, I take someone else (preferably Elain or Rutger). I level up Rutger or Dugal as the 2nd hero up to ~lvl 3

Weekly priority:
a) Wood and stone preferably on day 1
b) Town Hall
c) Bows, Crosses, peasants
In week 2, I take either Axel or Iris from the tavern (if the opponent has Academy Mages and/or Necromancer-mages, Iris is better). If neither is available, too bad, we level up what we have (though I've actually always been lucky to get either the schoolboy (Axel) or Iris)

Hero build 1 Vs Mages (Nothing stops a T-34 )
A) Education or Attack
B) Leadership-empathy
C) Luck-soldier luck
D) Light-Guardian Angel (mandatory)
E) Attack-Retribution or Education-Mind

Unit pick
1-Red
2-Red
2-White
4-White
5-Red
6-Red (White against Letos and other Black mages)
7-White
Hero build 2 Vs Dwarves, Humans, Orcs, High Elves (Pseudo-Necro )
A) Leadership-Empathy
B) Education-Mind
C) Defense/Attack (Depends on enemy Heroes)
D) Light-Mass haste
E) Darkness-Slow Confusion (-Weakening strike)

Unit pick
1-Red
2-White (Red against Orcs)
3-White
4-White
5-Red/White (Depends on quantity, White if few)
6-Red
7-White, Red against Orcs

Hero build 3 Vs Necros
If the opponent takes Naadir or [someone] based on the shout, I change race to High Elves (because there will be an ult 100500%). If not, Build 1.

Useful tips
We are vulnerable to rush; they might bait us into a Fort or unplanned army purchases—basically, they might try to shake the Economy, so in the Castle, everyone is always on edge.
Gold! Everything depends on it; sell unnecessary artifacts, take only gold from chests. You MUST build the Capitol FIRST!!! Use up peasants, capture the gold mine faster than anyone... BE A MAN
Build training grounds after horses
Don't upgrade Inquisitors, Angels, or Griffins until the last possible moment (until the pressure is on). If there's an option to upgrade and immediately buy Archangels for the main hero on the same day, go for it.
Build the Mages' Guild alongside the hero (lvl 15 hero = lvl 5 M.G.)
Buy up priests, make horses.
Dragon riders, neutral castles, mines must be controlled by you!!!
Don't carry extra artifacts with you for long; that's just wasting money.
Keep 2-3 heroes lvl 5-9 by the 2nd month!
1-Scout with Logistics; don't let them wander further than 3 days' travel from the main hero
2-Elain stays in the castle with diplomacy, experience trainer, and peasants; her job is to collect/kill weekly neutrals. Buy un-upgraded peasants, and you can buy her priests in combo)
3-Messenger, kamikaze, multi-purpose lvl 3-6. Primary functions:
a) Crash and find the exact number of creeps
b) Spot the artifact maker
c) Take artifacts from the main hero and sell them, transfer army to/from the castle.
Time plays in our favor, especially against mages.
FEAR the Necro ult because it counters you to pieces (if you're going to fight them, stock up on tissues )
If there's a mentor, you can hang out with diplomacy up to lvl 18. A 2nd hero who joined the heresy for free can diversify quite well.
The only chance to kill a Necro with an ult (usually Naadir, or the one based on the shout, I don't remember the name) is a very strong and fast rush.
Don't carry griffins with you; even for Iris, buy them last, save them, they carry (just not the red ones )
Don't run after Rushers and other heretics with your main hero, losing your head ...Walk the map with your head held high, comfortably, remember YOU ARE RUSSIAN! Even if you're a black mage... then you're a BLACK RUSSIAN!

P.S. Sorry, the smallest map I've played was Dragon's Pass. I.E., on small maps, my tips probably won't help. Last time I played was in 5 about 1.5 years ago, maybe I forgot (confused) something. But it seems all okay.

"+" if you liked or the tip helped.
Thanks for your attention and Good Luck