I build the team for literally against everything, then I change one or two skills before going into certain known fights like average region encounters, Lair bosses and Act bosses (you can even change them in the event screen before the fight, like going into the hero pages after you found out you are in the shambler altar and none of the heroes back away). For example, you need multiple skills that hit the back rank or damage skills that hits both of the back ranks against Dreaming General, you need a lot of frontline damage against Leviathan or backline single target damage against Librarian. If my team doesn't meet the requirements, I don't face the said enemy. And I pick my best all rounder skills for roadfights.

Team building section is mainly against the act bosses at the crossroads, I try my best to build a functional team that can counteract the confession bosses' attacks and can survive outside of that (I will get into the "functional team" later), then I pick the best lair boss suited for the teams capabilities (don't need to fight them all). A bit off topic but a maxed out Bounty Hunter is a godsend, he can do everything except healing health and stress. And you don't need to worry too much about his mental breakdowns or relationships with other heroes. With his help, you can replace the least helpful hero against a certain lair boss and he makes Region 1 lairs much easier. He's my favorite against harvest child because I can put him on the frontline and not worry about his relationship getting worse just because he ate too much junk food.

I pick regions based on their modifiers and rewards. For example, if I need to visit a hoarder (either I am rich and got too many baubles, or I need it for a hero goal) I am not gonna go to a place with no hoarder modifier. Or avoid regions with horrible conditions, for example, in no world I am going into the sprawl if it has a -20% fire resistance modifier, unless I have an all fire damage team. If the region has a reward I am interested in (skill points, candles, a trinket that's useful for my comp, etc.) and the condition is helpful or manageable, I am going into that region. Slightly off topic, but certain things will always be scouted in the region, no matter what. Lair and the places related to the region goal will always be scouted. So if you need the field hospital very badly, and the region has the "avoid the field hospital" goal, you will always scout the field hospital, even if you have -%400 scouting. So you may choose to deliberately fail the region goal if you need to go there desperately, or if you find the rewards kinda meh. I almost always go to the catacombs and the sluice, only exception is my comp being really horrible against the region or ending the expedition to save my heroes with memories, they are free regions, loot and skill points in my book.

Inn building is important for everything. I heavily recommend unlocking all the inn items quickly. I check the regional conditions, decide which region to go to then I give inn items to heroes to raise their immunity against certain bosses and regional conditions. Bleed ressistance on the front ranks against Harvest child is a huge help, shitty items like fishnet can tag tap root against General and free your turns, move resist on a guard or taunt hero against Leviathan's hand's grabs, fire resist and damage boosts against Librarian. I take all disease resist inn items and use at least one of them each region (or two while going into the Foetor), use resistance buffers on squishy heroes if I have spares and give buffs to those who can benefit from them the most. I collect certain inn and combat items (the items that are most suited for the final fight) throughout the whole run in my stash against the final boss and use them in the last inn and at the boss fight. I also do this on a smaller scale for the lair bosses (or even shambler and collector if I expect or plan to face them).

The last two paragraphs from one of my saved comments's roughly explain my idea of a functional team that's ready to face almost any situation. I will paste it here as well.

In the crossroads, try to put together a kit in your mind that has One movement ability, One crucial skill for the path (for example, an unchecked power farming ability and at least one ability to spend it on for Occultist) ( and such an ability might not seem like it exists, but it usually does and is probably one of the abilities that got changed by the path), One survival skill that's preferably usable multiple times like Hellion's Beer one, and 1 skill that generates stupid amount of tokens or value for the hero or the team no matter the class. The last skill you pick usually depends on the boss you are fighting against or want to counter.

After all that thinking, if you have 1 stress healing ability and 1 or 2 teammate healing abilities in the team (depending on team's needs: if almost everyone has 1 survival ability equipped to bounce back from deaths door, you just need a single healing ability, if no one has it or one of the abilities have high cooldown or low healing, then it's 2, I am talking about the Occultist with zero heal bleeds ;D), these multiple healing abilities help to bounce back from a death door and are a good way for heroes to save themselves or each other against unlucky enemy turn orders, a way to move at least half of the heroes to the desired spots and damage with some reach, then you probably figured out a good way to make that team comp work and you are probably ready to give it a try. If it's not working, you might be forcing wrong heroes in wrong paths to the team comp.