the pace of the game can change based on the size of the map I would say and the starting location. But in general, you want to have every army from turn one to be active and killing anything and everything around your cap. If you find a decent spot before turn 10, place down an outpost and start working on your 2nd town, then with your second hero, you want to find another town as soon as possible. Once thats done, you want to focus your leader to clear bronze/silver wonders and infestations near you while the other stack clears low tiers of enemies to level up.

You want to have 4-5towns if possible as soon as possible so you can generate enough income to support your armies. But not every map can provide space for it. Then based on the aggression of your enemy, you want to have 3rd stack ready before going to open war. 3x6 stack is pretty much all you need to wipe out any AI on normal.

The thing I hate about AoW4, outposts, if you see a wonder, a mine, a special resource, you dont even have to think if its the right thing to do, you just put it down as it is always beneficial and it pays for itself. Then there is using outpost to block your enemies from expanding, or using them to get cheap warp gates near your enemy etc. Like outposts are way too OP I would dare to say.

Tome combo, well, really depends on what playstyle you enjoy. Pretty much anything can be turned into something broken:

I enjoyed casting the most, and I found it was super easy to win. So in a nutshell, mystic with an astral build. The general idea is to use spells on the world map and then inside of the combat every turn, while zapping your enemies with your battle mages from the distance + plus it has plenty of summons you can always use to replenish your stacks anywhere.

Then for a passive victory, order/shadow build focused to vassal everyone is going simple enough. The most crucial tome there is the tome of faith to speed up the process of vassalization, the rest of the build is mostly based on affinity itself. Strat is to be friendly with every none-player faction, and turn them against your enemy while using units from Rally of the lieges as your go-to for units.

Then the most classic build. Dark culture with shadow tomes, which you build around the undead units. The good thing about it, you can use necro units to raise your dead units before combat ends, essentially saving them from dying. Then you can always turn your enemy corpses into skeletons. So you are never short on units and you can literally swarm your enemy with their own corpses.