I know what you mean about pKreoss, he's kind of addictive to play

pSevvy, good choice though. He's a wonderful generalist who can work with just about anything (as long as he has an Arc Node).
Now, as for Bastions vs Cinerators, yeah Bastions are usually considered better, if only because Cinerators rely on enemy attacks to get their speed buff (and the enemy might not oblige) and while they hit harder, the Bastions Reach and Blessed usually have more utility.
Knights exemplar are good, but they're a second line infantry due to their stats and low threat range. They mostly fill about the same roll as Bastions/Cinerators in that regard, cheaper and more of them but easier to kill. They are great tin can openers though, and great if you can keep one or two alive some how as they hit harder as more die (The Vessel of Judgement Battle-engine also works well for them, as it allows them to get a few more hits out as they die). If you're trying to be frugal at the moment, probably only grab either bastions or Knights Exemplar, because of the role overlap.
Exemplar Errants are one of the staples of Protectorate lists, and are brilliant. With their U/A they have a suite of abilities that make them a great toolbox. They can do a bit of everything, melee, skirmish and tarpit. They do have some overlap with the Temple Flame Guard however, the
TFG tarpit better and are faster, but you generally don't need both in a list, as they compete for Defenders Ward. However, because they have quick work (charge and kill something, get a free crossbow shot) they do work very well with Kreoss' feat, and can often kill two models a piece on feat turn if they get the opportunity. I'd generally take them in a pKreoss list if I had the points, but if you wanted to expand the list a bit, I'd probably choose something a bit different as it would usually be them or the
TFG rather than both. They should definitely be on your "to buy" list at some point however, as they are well worth it
The Senenschals all fill different rolls, and their value is very subjective.
The Errant Senechal is really only useful if you have errants in the list (which he grants Hunter to). He's nice, but he's not necessary, and it can be hard to find that two points which you're not spending on "essentials". If you face a lot of circle or other factions that use/generate cover and concealment however, he's really nice to have.
The Knight Exemplar
Senny has a lowish threat range, but he's great for two things - holding objectives (because he simply cannot die until after a turn is over

) and beating up jacks. You mostly see him in
eKreoss lists, but he can pop up anywhere. The only thing is that he's competing with Nicia for his 3 points, and she's dead sexy

though she's more of an infantry killer of course.
Bastion
senny is... too new, I don't know much about him, but I'd speculate you could take him with Bastions and a Marshalled Repenter, and he'd be decent enough.
So anyway, in terms of Jacks I'd still recommend a Rekoner kit and a Redeemer. Units wise, Daughters would probably be a nice complement to what you have, but anything mentioned so far is pretty good to get. Also, Zealots might be a good idea, because (as I mentioned) they need no caster support, so they make a great second tarpit in larger games or for casters who don't support infantry much, and both Kreoss and Sev can make good use of them in a 50pt force when you get up to it.
Edit: Crap, I just saw how much I wrote... sorry for the wall of text there, hopefully it's helpful though.