So it took me about a dozen tries before I figured out what I'm doing (I didn't come looking online for help). I finally sat down and figured out a bunch of the math that drives the game, and have assembled a pretty good team. I'm waltzing through PotD, which I switched to because normal difficulty was trivial.
The most important thing to realise is that, while it looks like it encourages balanced character builds, with every stat having some impact for every character, the exact opposite is actually true. It uses a flat probability distribution, so the marginal impact of each point in a combat stat is greater than the previous point. This is especially true with Dex: the action speed it describes affects everything, including your cooldown time from your last action, which hits 0 at +100% speed.
To never be hit by an opponent, you need a defence 50 points higher than their accuracy, to avoid grazes it needs to be 85 higher. Just having lots of hp is pretty much not worth it, since most of the time you'll lose to detrimental status effects rather than HP attrition. If the first enemy knocks you prone, his friends get to pile on with a +20 to hit. Relying just on HP also means you'll have to rest much more often, but that may or may not be an issue.
To be able to score criticals, your accuracy must be at least 1 higher than the targeted defence. Once again, each additional point of accuracy reduces your chance to miss more than the last point did.
Since you're planning to use the default companions, turn off the option in the menu to have them autoleveled when you recruit them. They still start at the same level, but you get to go through the levelup process from 1 on, so you can avoid the bad choices they otherwise take. You don't get to pick their stats or level 1 stuff, but you do get to pick the rest, without paying for retraining.
As for your main character, Cipher is probably the most flexible choice. Rogues don't get good deflection, Paladins and Fighters have a hard time affecting the battle more than a couple feet away. I'd also suggest taking a closer look at Chanter. Its deflection is almost as good as a Fighter, and like the Cipher, it can cast spells all day. The major drawback is it can't cast the spells right at the start of the fight, but it does start chanting, which at low levels can render foes pretty much incapable of hurting the party.
I recommend pumping dex as much as possible, and resolve too. Resolve is the most important stat for the story, and maxing it gives you a 9 point deflection bonus. Might isn't super important, but don't drop it below 10. Perception is also very useful in the story. I usually dump con, but keep in mind it is important for your fortitude saves. When it comes to your class abilities, anything that boosts deflection is good, getting your deflection up to around 90 will keep you from getting critted. Anything that boosts action speed is also not bad. For offensive skills, runner's wounded shot is probably the most powerful of the cross class abilities. It does a lot of damage up front, 80% more after a few seconds, and slows the target. I usually get it on every companion, which lets us take out the soft targets at the back of a pack at the start of a battle. Keep in mind you can only have one modal combat skill active at a time, so grab the best and don't waste points on the rest. For skills, get a few ranks in survival, and at least one in athletics. Athletics is one exception, where each rank is less valuable than the last. One point in it gets you a fast 20 point heal, each rank thereafter is more expensive to buy, and only increases the healing by 5. Once you've got those, pump lore, it is needed in conversations and none of your party members can take care of it for you. For race, I usually go pale elf, the 10 points of DR against fire is super nice, and stays relevant the whole game. Moon GL is not a bad choice if you're up front.
For your companions, Eder is a pretty good frontliner. Give him a hand axe and a shield, and take anything that boosts deflection. Guardian stance is very good, since it gives a 10 point defence boost to all allies nearby. It doesn't explicitly mention it, but Eder gets the bonus too. Having it active does mean he won't hit super well, but when that starts to be a problem give him a flail, which will let him convert 30% of his grazes to hits.
Aloth makes a great second liner. His defence isn't good enough to want him up front, but between Deleterious Alacrity of Motion, any of the displaced image spells, and Concelhaut's Parasitic Staff, he can attack from the second row, with a lifesteal attack, and is reasonably well defended. The best part is he can do so a bunch of times a day, since it is a very efficient use of his spells. When he isn't needed up front, give him a wand. For skills, have him grab the one that makes wand attacks AoE, then stack the DR bypass.
Kana's stats don't really make him frontliner material, even though he is a Chanter. I usually put him in the back with a couple guns. An arquebus has good DR bypass, and he's got good enough accuracy to let him take out priority armored targets. I recommend a blunderbuss for the second, which is crap against armor but can wreck mages really well. For chants, the one that boosts reload speed is a must. For spells, the summon phantom is amazing, toss it behind the front rank of enemies to give Eder flanking bonuses. The white worms are great for dealing with champions, wait till all the other critters have been killed then detonate the bodies, it will usually finish off the tough guys. He also gets a level 2 paralysis spell, which is absolutely amazing. With his int, I often get 15-20 seconds worth of paralysis, which makes it easy for your other characters to pile on the damage.
Sagani also isn't suitable for the front line, but she has impressive accuracy and high Might, so her damage output is good. Mostly I boost her animal companion, higher DR, plus higher damage. This puts him alongside Eder on the front line. I give Sagani a pistol, which gets her the DR bypass needed to kill the armored targets Itumaak is attacking.
Sagani is the last character I bother to bring along, so you'll either need to look elsewhere for advice if you want a 6th, or extrapolate for yourself.
For gear, Aloth does fine in his original armor; the overseeing property is too nice to give up. Eder also stays in his armor, since the ability to bounce back up in the middle of a fight is very nice. I put everyone else in the heaviest armor I can get. This largely offsets the speed bonus from pumping dex, but it does mean you've got 12 pts of DR, while attacking at the same speed as someone in leather armor. Also, grab the blunting belt from the blacksmith in the first town. It's expensive, but totally worth the price. The pistol I give Sagani is the Disappointer, it starts with the quality enchantment 'Terrible', but you can replace that with Fine at level 4. It's base damage is the highest of any pistol, so once you enchant it, it becomes a powerhouse.
