I’ve retired my company in Battle Brothers after 365 days (because achievement). It was a Veteran/Veteran/Ironman game, though it wasn’t true Ironman as I would use the force-quit trick to replay some battles that went exceptionally poorly. Without that trick the run would have ended much, much sooner.
The run completed all three end-game crisis events, and at the time of retirement, a second greenskin invasion was happening. The witch’s hut major battle was beaten, but I could not complete the goblin city, black obelisk, or kraken battle. The reason I couldn’t beat those battles mostly came down to not having a massively min/maxed set of brothers, as I finished the campaign still using a mix of starter backgrounds along with some un-optimal higher-tier backgrounds. I’d say I had maybe three brothers who I would consider top-tier in terms of stats.
In terms of gear I had about 10 named items, along with full sets of high tier weapons and armor. The room for growth in this area was pretty slim, basically limited to more and higher-quality named items.
I’ve started a new campaign with the intent of seeing and beating all of the end-game content. Due to this, the run is not ironman, and I’m save scumming recruiting hard (buy everyone in a city, check stats, reload and only higher top-tier recruits, if any), as well as reloading any battles that go poorly. This of course leads to the game being overall easier, but that also means I’ll hit the power needed for those end-game battles faster. Once I see and beat those, I’ll retire the company and, most likely, start a true ironman run where I don’t use the force-quit trick, and just play until the company is wiped out.
Hardcore Casual 
If keeping the melon ‘mugger’ till endgame is wrong, I don’t want to be right.
I had trouble recognising what good stats even were
The min/max consensus is for frontliners, you want to always put points in mAtk, mDef, FAT. Backline is mAtk/rAtk, rDef, FAT. That’s for heavy armor/battleforged guys, which will be most of your brothers.
Nimble build you focus HP, mAtk, mDef, with the idea being that since you are in light armor, your FAT is fine. A subset of Nimble is the fencing sword, where you want max INT (130+), trading mDef to get it (dodge will give you a lot of mDef/rDef). Archers are rAtk, rDef, FAT, using lighter armor and Nimble.
A good end-game recruit starts with 60 mAtk and has 2-3 stars in it, so you end at 90+ mAtk at lvl 11. mDef you want stars in as well, starting amount should be at least a few points, ending at 35+ at lvl 11. I don’t recall suggested and end-point FAT values.
The above however doesn’t really take into consideration the number of battles that now require higher Moral with the DLC. Some people simply avoid those fights, others have backup brothers (late-game) that have more points in moral just for those fights. I don’t love either solution, but at the same time points really are tight if you want top-end brothers for the hardest battles.
that’s great, what about talents? I usually end up taking the same on all my brothers (e.g. 25% health and pathfinder)
This is a nice tool: http://tumult.cc/bb-calc.html
Here is a basic frontliner build, putting in whatever weapon mastery you want (this assumes its a 2h brother): http://tumult.cc/bb-calc.html?1-3&1-9&3-4&4-6&5-4&6-4&6-1&7-3
Gives you 2 extra points. I like Steel Brow and Rotate, but it kinda depends on the points you have and if you need to fill gaps. Low mDef, get Reach Advantage. Headhunter is viable, Indomitable is good, etc.
Nimble build is something like this: http://tumult.cc/bb-calc.html?1-9&4-6&1-3&5-4&6-3&2-3&6-1&7-3&1-8&7-2
Can swap some of the offensive skills (frenzy) for defensive if you need based on stats.
i was disappointed to read that you must absolutely min/max your brothers and boot the one who are not perfect roles. I get attached to my brothers and love to have the cripple banging heads. Too bad, i think i’ll pass on the expansion if that is the case.
Well you had to do that in the base game to beat Gobbo city or Black Monolith. With the DLC that also now applies to the Kraken and the Waterwheel. But if you don’t want to min/max that hard, those fights are optional, and while cool, certainly not the main meat of the content.
Also in a bit of an odd twist, if you go the mAtk/mDef/FAT build, you then kinda struggle vs the new enemies in the DLC, while if you go more general build, you fair better (mostly based on having higher resolve)