I read a lot of complains about the difficulty increase in chapter 3, but I went through without too much trouble (I just moved to chapter 4) at max difficulty. Here is what I think helped:
- Grow tall, not wide
You are constrained by 2 things: number of groups/available characters to send on mission and resources.
It means you need to make sure your characters don't spend too much time recovering.
But it laos means you need to make very good use of your resources to help with that.
The best upgrade by far are more parties with more characters, but that cost a lot of resources, as you need to upgrade 6 buildings between each level of stronghold upgrade.
I think the best way to do so is to just forget diversity and focus on as little weapons and classes as possible. I went with:
- Armors: Crusader and duelist almost exclusively (you can field 2 of each, and they both have easy access to taunt).
Rationale: I don't care much about the armor of the other: the petmaster has a pet to tank for him. Alchemists, archers, and gunners should avoid getting in harm's way instead of wasting your precious resources. 1 armor upgrade here and there can be ok, but don't overdo it
Weapons:
- halberd (best AoE power in game), works for crusaders and duelists. I give one to all duelists.
- poleaxe (ie, giant hammer): not sure it was the best choice
- greatsword: Very versatile. Not sure it was not redundant with poleaxe and halberds
- sword (but I don't like 1 handed weapons much in the game): dagger has no business being a main weapon, hatchet will turn the enemy to your direction which is exactly what you don't want to do with duelists. However, it means petmaster weapon won't get upgraded.
- bows (I went with bows, because 3 classes can use them, but crossbows are still OKish, it's just that they are probably not worth investing on early)
As in XCOM, staying alive is mostly done through killing opponents, so I didn't increase shields at all (and seldom use these to begin with).
- guns: arrive much later, but best ranged weapons IMO.
Alchemist:
skip every specific ailment remover. I just use crusader to delete debuffs, and stock on health potions. Later on, incense of heal + all debuff removal is a good choice.
Enhanced balms are a must have. Most other items should be skipped
Stick with 1 single kind of arrow and upgrade it. I went with fire to ignite the alchemist surface.
Invest all you can into building improvements:
- Barracks makes the most difference. recruiting high level characters for cheap makes your life much easier.
- Prison can provide more passive bonus
- Forge and alchemist when you can afford some of the upgrades (typically, after you need with imbalanced resources, it may be a good time to upgrae crusader armor/weapons).
Important class skills and other considerations:
As with all similar games, action economy is everything. You can usually spend some time setting up before a fight, so buffs are not that bad, but they only provide 1 turn of benefit because you should never use them instead of wrecking faces.
It is always better to select the skills that give or deny actions over others (hence why AoE melee weapons are the best!: halberd AoE attack can give you 4 attacks for a single AP, without cooldown if you have 2 opponents in range).
You can make the AI do stupid things with hazardous surface, but the nature of the hazard doesn't change much. I like the alchemist fire surface for that. They don't care as much about the slowing surface, though.
That is also what makes archers (whatever the class name is) great:
the free item slot per turn can be use to great effect with a special arrow, granting them a third attack, or a siege engine if there is one nearby.
That means lonewolf is also much, much better than caltrops, because it applies to each of your attacks (and you already have the alchemist do to the same).
Alchemists work best with a focus on either healing or damage. I haven't tried damage much, but buffed acid potions seem like a good alternative to bringhing a hammer crusader to deal with armors.
Crusaders can go whatever you want, and mix things from both side. I think removing debuffs is much better than self healing (they have the highest armor, and healing is the job of the alchemist in the first place). Also, recovering armor is good!
They have great armor and survivability. I lost 1 of each other class (but duelist), but never a crusader. Don't waste them by putting a shield (also, it would be ahistorical to do so; it is plate armor OR shield when not on horseback!). Taunt is their bread and butter: They cannot prevent an engaged archer from shooting, nor can they prevent an armored opponent from ignoring them to whack your backline. That is why taunt is very very important on them.
For duelists, both options seem viable, but I wouldn't take the skill that waste an action to multi taunt (haven't tried it, though), over the one granting free AP/MP on kill/backstab. I think a single taunt is enough, and more crits is great, because you'd rather kill opponents than hope you can parry them while they bring reinforcements.
For beastmasters, coordinated strike is a must have, even though marked looks great, a single coordinated strike with a bear can almost delete most opponents.
I have found the bird underwhelming.
Unlike in XCOM, if you heal before heading back to town, you will have less downtime, so make sure to do so, and load up on potions.
You can randomly meet characters that can be captured, even in non capture missions, so always bring shackles (except for storyline missions, where there is no random opponent).
A missed capture is 200-800 GP wasted!
Losing characters is OK, replacements are cheap, and no one is unique. A maxed barrack lets you not to lose much in the porcess. Note that weapon training is valued higher than level for replacement.
As for turn limits, if you focus on killing opponents (as opposed to kiting or whatever), they should never be an issue. Even before the patch changing them, I never had any issue with them. Sometimes, the assassinate/free character and extract missions can be a bit tough, as characters that just get there as reinforcement may tarpit your own characters before they can reach the skyranger for extraction.
You should just make sure that you don't end within 1 move range of the reinforcement area the turn before you want to extract. I usually kill every one in the first pod to spawn, then get out.