So the first turn of the game, you will have a Spartan (with the Justaerin and Medicae), two Contemptor Dreads, and a Typhon Siege tank? Four models in total? What Rite of War will you be using?
Couple notes:
Veteran's no longer have Marksmen, it's now Scout. (see
30K FAQ. You might want to rethink the all combi-plasma's in that case. Those guys ain't fearless either, and nothing is more frustrating then losing a 3 guys in a 10 model squad and failing that morale check. And it's even worse in close combat. Every squad should have a Vexcilla.
Interceptor works on anything that arrives by reserve rolls (like deep strike, outflank, the Subterranean Assault rule...). And of course Augry Scanners are fantastic for a free round of shooting at deep striking units, but also pushes any infiltrators or scouts further away from you.
The great thing about SoH is you are able to play this style of list. Other Legions get pigeon holed into a particular style of It's not even close to my style of list at 3,000 points, but this list could work. You should be a little concerned about objectives, as you only have four squads that can take them. The Justaerin are the brute squad, meant to take on another brute squad. Anything else and you are wasting them. So really, you are depending on three ten model
MEQ squads using reserves to deploy onto the table and take objectives. I love Justaerians, but I'm not sure how your Brute Squad will fare against another Spartan + Brute Squad + Primarch. At 3,000 points, that's the standard. Spartan, Brute Squad, and Primarch.
You could shave some points off by using a couple Sicarian Arcus tanks instead of the Typhon. They will definitely have more shots and maneuverability at the price of durability, but this is 7th edition. One lucky Lascannon shot and any vehicle is toast. Or, you could use say an Arcus and Venerator and still have points left over. That way you would get both one of the best tank hunters (the Venerator) and good anti-infantry.
The Justarieans are listed as 10 models, with 3x Power Fists, 3x Lightning Claws. Are the other 4 just combi-bolters and a power weapon? You might want to look into a chain fist or two, and definitely get a multimelta in there. Maybe a combi-melta or two as well for the charge? Just remember, power fists, chain fists or anything that strikes at initiative 1 doesn't benefit from Merciless Fighters.
The Primaes Medicae and 1 Apothecary- I wouldn't even bother with Power Weapons. If they get into close combat, something has gone wrong. You might want Artificer Armor and an Augry Scanner instead.
On the Lightning: Battle Servitor Control seems redundant when you are running it with 4x Kraken Missiles with Armorbane. The Ground Traking Augries (Strafe special rule) has so many exceptions, that it's not worth it in my mind, especially when the aircraft is BS4 and comes with
TLLC. Most of the Lightnings I see are always equipped with the Ramjet Diffraction Grid. That's one of the best defenses you could put on an aircraft! With so much anti-tank already in the army, and with two Contemptor Mortis dreads, what's the purpose of the Lighting? What you need here is anti-infantry, so instead of the Kraken missiles, maybe Phosphex Bomb Cluster or Electromagnetic Storm Charges would be better? Or, as you suggested, maybe three Javelins would be better?
You really are lacking in bodies, and I think you will struggle a lot against Custodies which are built for destroying low model count, elite armies. In games with objectives, you will be facing an uphill battle. Deploying your only scoring units by deep strike and outflank means it'll be a foot slog for them to get into position. Last thing: You are not playing to the one strength of SoH: Mercilious Fighters where you get an extra attack in close combat if you outnumber your opponent. That's not a bad thing, as you more than make up for it in shooting, but you are lacking in the close combat department.
This is a unique SoH list, and I'm really curious how it functions on the table! It should do well as long as you keep your opponent at range. Good luck!