The build relies mostly on killing with summons, and on an important fact: in turn-based, Vela STAYS STILL even without being terrified, IF she stays not terrified.
So, for a typical fight, take the Tortuk fight on the Dunnage docks. I send my boar (boar is huge because it regenerates after getting knocked out nearly every combat) to attack one of the powder monkey adds, while my MC is sneaking far away over to the left around a sort-of-corner by the steps of the deck (not pier). I learned the hard way to suicide my boar rather than to try to save him. Trying to save him draws enemies near myself and/or Vela, and they coded Vela in an extreme sort of way, where she runs into combat way too insanely, and enemies do target her sometimes. So, my boar will use its movement to run to the right, even farther away from me. The enemies will head after the boar. For this fight, I might be lvl 11 with upgraded Wurms and also normal Ogres. I move forward on my turn (half movement dots b/c in stealth), and summon wurms as far from myself and as close to enemies as I can. The actual summoning spell finished on turn 2. As opposed to Ogres, Wurms tend to get initiative right after being summoned. This is important because it means they can move closer to the enemy right away before the enemy moves closer to them, which prevents creep of the fight getting closer to Vela. Now, the enemy is basically locked. If they have the firepower to kill my summons before I can make more, then I stay in stealth and I am fine. Nearly always, they cannot kill my summons, so I leave stealth and help fight a bit with a 2h ranged weapon (or not, if I don't want to have decay of the weapon for no reason). However, I use my judgement and don't leave stealth until the fight is under control enough so that I won't get enemies messing with me. It would be very bad to be out of stealth and get interrupted while you are summoning, and be left with no chants and no summons. However, there are a million belt-items that can summon 1/rest for emergencies I always keep a fresh one handy. It is rare I need to use one.
20 int with items is a magic number, btw, for duration in rounds, especially once you get lvl 19 with ancient weapons. 15 int is enough for resummoning Ogres and Wurms. You only need to use the original skeletons in the first cave, since you can get to lvl 4 before the digsite fights.
The only active ranger abilities I use, and very rarely obviously (since they are per-rest until and unless you get brilliant of course I do a no-rest run for all the bonuses and for Eothas time), are marked prey (non upgraded) and evasive roll (which is awesome sometimes mid-combat when Vela is safe). Passives are things like resilient companion, 2h weapons, Marksmanship, shield, concentration, and then you have have so many extra talents that you take stuff like extra weapon slot, fast running, and 1-3 of the +10 saves ones, since why not. Definitely take survival of the fittest, lucky, toughness, and such. None are breakers, but they add up and few talents are critical. Once you get ancient weapons, you still want to have upgraded wurms, and that is all you need. I don't use other invocations, but somebody might find some narrow use for a damage one. Chants, you mostly want ancient memory and at lvl 20 the one that makes skeletons (which don't unsummon your ancient weapons, by the way). 15% fire damage on weapons is useful a little bit, and dragon wailed is almost irrelevant but you may use it a bit.
Dordugan is a somewhat special case, as you have to beat him yourself, with the chant-skeletons. Because of how this all works, it has to be in real time, so Vela has to get terrified. You start with Vela in the bottom right, and use your boar to start combat and lead Dorud close to her to get her terrified, then shoot him and lead him to the other side of the map. It is then easy to keep him far enough that his massive range abilities still don't ever hit her. Otherwise, he'd be fully impossible, but once you do that, you fight him a lot like Kaylon did in his video on youtube. Because of Abydon's challenge, you'd want 3 good ranged weapons and would need to kill him before they break. For this one fight, you'd want the invocation that gives you str and +2 pen (among some other stuff - forgetting the name of it) since that means you can pen with other ranged weapons (not just the Essence Bow) along with the marksmanship ring. And of course the cloak that heals you from fire.
So, your own abilites don't matter much. I wouldn't ditch anything too strongly, although maybe dex can go down pretty far. You need enough int to get to 20, and maybe to 25 eventually would be good. Perception for traps and hitting. And enough con to not die to stuff that hits you sometimes like the undead dragon. I had 10 might for this build, but I'd try to go higher for Dorudugan if I could. Resolve can probably be ditched, but overall it helps to not be overly squishy sometimes (such as against the water dragon and the risen undead dragon). There are a lot of fights in the game, and not all can be handled from stealth. When getting Revku's burden cloak, for example, you get ambushed by fire bats and a naga and stuff, and you need to help in the fight so that Vela isn't killed.
Turn based combat pulls more enemies, from farther away, than real time usually does. For example, in the hanging sepulcher, I started combat in that room with the risen guys, and the darguls and shade actually joined the fight, but for some reason the wraith stayed out of it. Still, this build is so powerful in situations like that, that I beat all of them, or rather, my Ogres and Wurms did (however, I believe I was lvl 16 when I did that, which is fairly high level). Wurms are great when you want to take down low-hp enemies who are in back, like Risen Archers and that Priest and such. Ogres have a ton of hps and once you have sweeping attack, that is really good for lvls 16-19, which can involve a fairly large amount of non-boss but not easy fighting, including some bounties. I beat that goldpact group bounty (Beina, I believe) who also has that ironclad, for example, as well as the 4 guys with the treasure map pieces, as part of leveling up.
In the cave with the bog witches in outcast's refuge, I did real time and that way didn't pull the witches in the farther room, but in turn based they all jumped in. So, as I said in my first post, I keep aware of the benefits and drawbacks of turn-based and of real-time and switch as appropriate.
For a pet, I use the animancy cat mostly, and for some fights like the Beast of Winter, the troll that makes you immune to engagement is great.