I don't play usually play 50pts so it's kind of uncharted ground for me but I would definitely want a another unit or two at that level.
A couple of thoughts;
The Mcthralls are always useful and like you said the Necrosurgeon. Don't rely on the Surgeon running around the field healing stuff as she can only do that or create Mcthralls in a single turn. Don't get me wrong it's nice to have a medic but in practise it doesn't really come up much (not for me anyway). The only time I've used her heal was with Skarre who uses her own life source for boosting and stuff. So I took the surgeon specifically for that.
Solo wise I rarely leave a Pistol Wraith or two out of my lists. They add great ranged support.
Warwitch sirens are good. I usually take one if I'm running a Stalker. Which I do a lot cause I love the little guy. A handy trick with the Siren is to whack a non-reach heavy with her sword, as long as she hits (don't expect her to damage) then the heavy won't be able to move next turn effectively making it useless for that turn. Another tactic not to rely on but it's nice when it comes off.
Gormans just good and you'll see him in a lot of lists. I tend not to run him as I just prefer to stick in faction. I'm probably handicapping myself but heh ho!
Aiakos is a decent solo. Have you considered running him without a jack? He makes a great super solo and keeping his Focus to himself means lots of boosting. He can play the assassination game himself if he's in the right place!
A solo you havent mentioned is the Skarlock Thrall. Very useful for saving focus and a bit spell slinging synergy.
Unit wise there's plenty of decent options, Bane Knights are brutal and can benefit from Tartarus, Bile Thralls are another favourite of mine and their purge attack is all kinds of funny!
Best thing to do it try a few options and see what works best for you. From my experiences I do find that Cryx have less auto-include options than other Factions as we have so many good options to choose from, which is nice!