Design: Hellghoul
Lesser demons can be brought into this world directly by Us, of course. The nastiest denizens of Our hellish home are always eager to make a mess of the mortal realm. But why go through the effort of bringing them directly into this world, when it's so much easier to stuff them into a pre-prepared vessel? Even Our pathetic cultists can arrange corpses, after all.
The Hellghoul is a lesser demon brought forth to reanimate corpses of the dead; human bodies twist and mangle and occasionally merge to accomodate the fickle soul of the new hellspawn. Most of those who come to this world so easily are ambitious, yet simple, making of their new bodies hulking brutes. Wielding huge clubs befitting their size and strength, the Hellghouls wade into the fray without a care for injury; after all, this isn't their body, so they feel no pain as they sweep the enemy from the field.
(Minor, inconsequential lore note: there is not, so far as anyone can tell, actually a 'hell' dimension. Demons exist on the mortal plane just like humans. This is inconsequential, because whether you are summoning demons from hell or creating them from scratch, the difficulty and effects are the same. (In terms of other dimensions, there are some. The Gods themselves seem to reside outside of reality, and the spirits of the dead usually depart this world for some form of afterlife (although spirits who are called back from the afterlife have no recollection of what it was like)))
Basic reanimation of the dead would be Normal. Using a Lesser Demon for this purpose does not make things (much)
harder, but it would make them more
expensive- you need more Evil to summon a Lesser Demon to possess a corpse than you do to just give the corpse motion and crude intelligence (the demon-possessed corpse would be stronger and more intelligent). This would be a Normal design, with the end result being Uncommon with a large unit size (~100).
Rune of Flame
Runes are a means of delaying the impact of a spell beyond the cast, and this Rune of Flame is as the name suggests - a spell that will make a delayed flame. When cast, the rune embeds itself on the surface targeted by the caster; the caster can then activate the rune when they wish, creating a pillar of flame around the rune. These spells can be cast before the lines meet, allowing the casters to open the battle with a flaming surprise as the soldiers charge towards one another.
A fairly elementary entrance to runic magic. This would be a Normal design, and the resultant spell would be Common.
Each creature in a 20-foot radius Sphere centered on that point must make a Dexterity saving…
Channeling dark magics, a spell caster can summon forth and cast a Dark Fireball. Upon reaching its destination it causes a large explosion of fire. This flame is mostly similar to normal fire, but tends to burn better on living flesh (and accordingly less so on “deader” things).
A 20ft radius is a pretty big explosion. While a basic fireball would be Easy, and the burns-the-living-more-than-the-dead aspect wouldn't by itself tip it over into Normal, the large scale would both make it Hard and, perhaps more importantly, make the end result Uncommon.
Runic casting
As fun and educating it is to have your spell hit someone and melt their skin or whatever, sometimes it's better to not be in the area of the spell when activating, by putting a rune on a surface or item a magic user can have the spell cast from a far by either invoking it or a trigger determined in the creation of the rune
Assuming that the idea is to make a system wherein all spells can be cast as a rune, this would be Hard. Runic casting would not modify the rarity of Magic Missile or Novice Ward, although spells that are on the cusp of being rarer might be affected.
What about a charm spell? Something called like dark seduction that our acolytes can use to very heavily increase recruitment rate?
While a more fleshed-out proposal would be nice, I can tell you that the basic concept you are describing would be quite doable, probably between Easy and Normal, and a Common spell.
The Gluttonous represent the lowest rung of an undead society: those who are permanently kept in a state just before death. The Gluttonous are mortals tainted by The Death of Suns and, being deemed unworthy of the gift of unlife, are instead cursed to an insatiable, withering hunger. This gnawing hunger breaks the mortals as their bodies weaken, resulting in The Gluttonous barely being able to shamble themselves forward. They desire food in the form of warm meat and death, and gladly seek both. The Gluttonous represent the current base of the cult's army, being extremely numerous and requiring incredibly low to no actual upkeep but are also a very imprecise and unintelligent tool.
This would be a Normal design, with the end result being Common with a large unit size.
Everybody knows those with wealth tend to have an unparalleled amount of political influence, and none are in control of more wealth than the banks. A number of vampires have come together to utilize their unlife as a means to identify, track, manipulate, and capitalize on various markets from the shadows. Their secret network of banks, the Blood Banks, are made to be some of the most secure locations available to store the wealth and secrets of even the most prestigious of mortals.
The Blood Banks make some money from secure storage of wealth, but their real income comes from extremely predatory loans of gold with incredibly steep interest rates targeting middle and lower class mortals. Material possessions can be used as collateral and are auctioned off for additional income once confiscated if the loan recipient fails to make adequate payments negotiated on a case-by-case basis.
So this is an odd proposal.
Banking: surprisingly difficult, actually, given a lack of capital or experienced merchants. Training bankers, finding customers, and building up the reputation and facilities needed to be an effective bank- Very Hard. (A more modest entry into the field could reduce the difficulty to Hard)
Sneaking In Vampires Like It's No Big Deal: Impossible. That is, a difficulty beyond Ludicrous. Obviously vampires are possible, but they aren't like a free toy in a box of cereal. I'd suggest splitting them off into their own design.