For Expeditions: Rome players, since I have played 70% of the game in insane ironman mode, and here I will share what might be useful for anyone looking forward to try this mode.
Money, resource, etc., should be no issue since the game has no timeline, and legion mission can be repeated to glean resource.
Conquer region is also easy peasy (legion morale can be maintained using stratagem, and army exp does not matter much). For army leaders in battle, I typically just use whoever gives me most loot.
For camp upgrade, I focus on the armory — forge — foundry path. As this gives you level 1 – 2 – 3 weapon / armors, and allow you to forge tactic items (pilums!). IMO getting the forge early in Act 2 is especially important for early-game survival; and foundry is more optional (because your Praetorian shall be good enough by the time you get foundry)
For other upgrade, speculator tent is certainly a must (to replenish the tactical items); the factory / arsenal gives you better stratagem, some of which gives better loot (for forging); all other upgrade are quite optional.
Finally, in Act 1, immediately recruit at least 3 archers + 2 veles at level 1 or 2. Refresh the pool (from camp) if needed, and make sure they haven’t invested in useless perks yet (see perk build below).
In battle, enemy are stronger than you in HP and damage, and will always use tactic items (fire jar / pilum / poison) against you. Luckily early game in act 1 they are on par with your Praetorian, while late game they can be 50% stronger.
Always equip any tactic item you have (everyone should have pilum, then equip some bandage / fire jar), and grab any free items on battle field if movement allow. Forge more tactic items until all your Praetorian have pilums.
Weapon upgrade is more optional, but do craft all the unique items, and upgrade any weapon / armor if you have resource.
Battle should be fast and quick. The more turns you have, the more damage you suffer. So in early game, this is achieved by 1. free pilum use; 2. kill the militia enemy first (enemy with a chess icon), so you get one extra action; 3. crowd control via the bleeding / harried / burning weapon effects that lower enemy damage, health, movement; 4. hold defense choke.
Then in late game, it will be easier — archers machine gun everyone, and Veles will solve any remaining individual enemy. See perk choice below
Other than story companions, additional Praetorian can be recruited from the camp starting from Act 1. I suggest recruiting them as early as possible, preferably at level 1 or 2, because higher level Praetorian may have perks we don’t need. At max level one can pick 19 perks, but more like 18–19 perks depending on the starting level.
The perk choice below is certainly not unique, but so far the most effective in my insane run.
Early game archer is a nice addition: their damage output is decent, high-movement, great weapon skill for crowd control (lower enemy movement, damage, and add burning / bleeding effect), at the cost of no armor and low health.
Then by late game they are absolutely OP and will handle most enemies in 1 turn. This is also my main char.
The Machine Gun build:
Hunter: quick shot (starting perk), versatile, skirmisher, arrow-stab, pinning shots (2 points only), barrage, find-weakness (9 perks)
Sniper: marksman, mark-target, walk your shots, seize ground, assist (9 perks);
Marksman tree is not needed.
In early game (before getting barrage), equip your archer with one bow & one melee, and pick versatile perk to boost your damage (it works well with the action point refund kill, as archers have high movement).
In late game, every archer shall equip two bows with normal damage skills (aimed shots / fire shots / crippled shots, etc.), and do not equip weapon skills that penalize your accuracy / range / damage (say half-draw). Also equip them with any Talisman that can boost min / max damage.
Once battle starts, click barrage — then you simply walk around and deplete all your skills: 1 pilum, 6 shot from weapon skill, 2 quick shot, 1 assist shot, and 1 more arrow-stab if you are lucky to get a melee. That is a total of 9-11 attacks in turn 1, about 100-160 damage, enough to kill 3-6 enemy per archer.
This is a great one from early to late game. High-damage throughout game, and the best character for killing enemy leader and finish certain mission types.
The Marathon Build:
Assassin: lone-wolf, cheap shot, sneak attack , assassinate, marathon, focus master, rush, first strike. (11 perk)
Duelist: born-ready, shiv, — (the middle 2 level can be any 3 perks), then quick-witted (8 perks).
Do not pick anything from brawler.
In Act 1 you can already get Sneak attack and Marathon, which is very OP for certain mission types. Once you have marathon + born-ready + rush, they become true assassins: click marathon, move to enemy leader, sneak attack + shiv, then use rush to refund your action, and strike again; or you may use duel, rush, then sneak attack + shiv. It will easily deal 50–80 damage on enemy leader in a single turn.
Late game Marathon Veles is worse than Machine Gun Archer in damage output, but archers are limited to movement and target sight and cover, while Veles can use marathon to reach anywhere in 1 turn. That is why I always bring at least 1 Veles to any battle.
They are useful in early game. Princeps are tanky and shield can absorb damage very effectively, and they can use the hunker down skill (from some shield) to completely block damage. I typically do the defender / vanguard perks.
Triarius can hit from range, and can heal, and there is a strong 5-hit unique weapon in act 2. Any skill route is viable. I always choose medic perks, then destroyer / flagbearer depends on the play style.
In late game under insane mode, their damage output is simply worse than Archer and Veles. So I rarely bring them after you have strong archer / Veles.
In early to middle game your team shall be relatively balanced to cover all your defense and heal needs. Typically archers (2) are used to slow down far-away enemy and finish nearby militia, Princeps (1-2) hold choke points, Triarius (1-2) will buff / heal / damage from two hex away, and Veles (1-2) will pick out individual enemies.
From middle to late game (act 2 onwards), archer with barrage will dominate the field. So I end up having 4-5 archers to solve most enemies in one turn, and 1-2 Veles to finish enemy leaders in 1-2 turns.
In story-based battle you are limited to your companions. With main char being archer, you still have 1 Veles + 2 Archer (main char + Julia), which is sufficient in my insane run so far.
Sometimes enemy will move first in turn 1. This may cause you to lose some archers before they can start hitting. Just load your save and re-position your other troops to take the damage. So long your archers get rolling, the battle is straightforward.