Alright, though it'd be good to know what you've bought so far so we can help get your lists sorted out
Firstly, the Errants are a great idea - they go very well with pKreoss, his defender's ward on them makes them pretty survivable, especially with their built in magic protection, and his feat means they can get a lot of good attacks out there (good charge, then quickwork for an extra shot). To really make them shine, many people take them with the Mercenary "Rhupert Carvolo", who can give the unit tough as well, and often the Covenant of Menoth to add in no-knock downs on top of that - these are good buys for any menoth army in time.
Now, the Paladins - they can be good, but if you take them, you really want to bring along Vilmon to make them good - without him, there are better 2 point options, but with him they're really quite survivable, and can be a real annoyance to opponents. So your options here would be to squeeze vilmon into the list, or to take the paladins out and put in a couple of other 2 point solos, such as a Vassal of Menoth perhaps?
Now the Deliverers... I'm not generally a fan of them, but pKreoss can definitely make them work. On feat turn they can be really quite good - 10 quite accurate (against knocked down models) long range shots into an opponent can be nasty. The only problem is that out of feat turn (and with most other casters), they're generally doing nothing but trying for lucky scatters onto light infantry, and not much else, which isn't great for the points. I'd generally go a unit of Zealots or Daughters of the Flame first in most lists, though as I said, pKreoss can make these guys work.
Now the Jacks a bit the other way around - they're all good at what they do, but they don't really help pKreoss all that much. pKreoss is a ranged assassination caster at heart (though he's flexible enough to do a bit of everything), and the best plan for him is to get him a bit of ranged power for the "pop-and-drop" - basically, try to drop your opponents caster with Kreoss' feat, and then shoot him to death.
Definitely take those Battlebox jacks when starting up (each of them is pretty good for their role), but where possible try switching out the Reveger and Crusader for a couple of our 8 point ranged heavies like the Reckoner and Vanquisher (you'll obviously need to find a few extra points to do so), or a Redeemer.
I'd definitely recommend getting a Reckoner kit early on, and swapping that in for the Reveneger, because while the Revenger is an excellent Arc Node, pKreoss does not need one - he wants to save his focus to give it to his ranged jacks for boosting. Also, getting a Vassal of Menoth for Jack support is a great idea, especially as he allows your ranged jacks extra shots on feat turn with his Ancillary Attack action.
So, taking what you've put down here, and modifying it somewhat, you could try something like these lists:
Option 1
High Exemplar Kreoss- +5 points
-Crusader - 6pts
-Repenter- 4pts
-Reckoner - 8pts
Choir of Menoth, 3 grunts and leader- 2pts
Exemplars Errant- 9 grunts plus leader- 8pt
-
UA for Exemplars Errant- 2pts
Vilmon -3pts
Paladin of the Order of the Wall- 2pts
Paladin of the Order of the Wall- 2pts
Vassal of Menoth - 2pts
Wracks - 1pt (Excellent focus support, well worth the point).
Option 2
High Exemplar Kreoss- +5 points
-Reckoner 8pts
-Vanquisher 8pts
Choir of Menoth, 3 grunts and leader- 2pts
Exemplars Errant- 9 grunts plus leader- 8pt
-
UA for Exemplars Errant- 2pts
Daughters of the Flame - 5pts
Rhupert Carvolo - 2pts
Covenant of Menoth - 2pts
Vassal of Menoth - 2pts
Wracks - 1pt
Option 3
High Exemplar Kreoss- +5 points
- Vanquisher - 8pts
- Reckoner - 8pts
Choir of Menoth, 3 grunts and leader- 2pts
Exemplars Errant- 9 grunts plus leader- 8pt
-
UA for Exemplars Errant- 2pts
Deliverers- 9 grunts plus leader- 8pts
Vassal of Menoth
Rhupert Carvolo
Now, these are just some rough examples for you, it's certainly easy to mix and match a fair bit. The only thing you need to keep in mind is that you have to balance how much infantry clearing you need against how much anti-armor you need, how much support you take with how much actual front line stuff you get, and have an idea of how your going to use all your pieces in your overall plan.
For expanding out to 50pts, I'd definitely take Zealots with a monolith bearer as a second large unit - they're wonderfully independant, but benefit hugely from Kreoss' feat turn to extract them from combat after their invincible turn. I'd also look into getting some more focus support (like a Heirophant, Reclaimer or Tristan Durant) and fitting in a Redeemer rocket jack.
Anyway, hope that helps, and here are some previous threads where I've talked about starting up with pKreoss:
http://www.dakkadakka.com/dakkaforum/posts/list/526909.page
