In Europe and its colonies the 18th C. is indeed a period of transition. Most people, specially in the lower classes and in the countryside, still are as superstitious as in the British Isles during the 'witch finding' / ECW age or in Salem at the age of the witch trials. But for a minority it is already the age of the Encyclopedia, of Enlightenment and emerging science. Thus for gaming purposes it can be treated as the time when declining magic is challenged by rational science still in its infancy. In the same way as magic is 'dying' in the 'Dragonslayer' movie (and somehow in Middle-Earth at the end of the Third Age); and the Old Faith (& magic) is fading and Christianity triumphing in 'Excalibur and 'Dark Kingdom: The Dragon King / The Ring of the Nibelungs.
Thus, while I'm generally reluctant to have 'real' magic and 'weird' science in the same setting -they are largely redundant in game terms, and are rival interpretations of what the uneducated sees as 'miraculous'- I'd make an exception for the 18th C., making the period all the more interesting - '
Lacepulp' (Fantasy) coexisting with '
Lacepunk' (Sci-Fi).

(Foundry female 'Revenant Elves' do have a 18th C. 'look':
their ears 'normalized' they could make convincing 'Lacepulp' witches -of the 'big foot' coven

)
Fantasy:
Witches, of course, and nor only in backwater countryside (the
Black Masses were nor so old, the French Court was ready to believe in the 'immortal' Saint-Germain and in Cagliostro,
Mesmer's 'cures' were largely perceived as 'magical'). But of course witches do NOT have to wear the
Disney™ Halloween regulation uniform. Besides, witches are *
beautiful*: they look like old hags only when wanting to pass unnoticed.
Werewolves are part of the European folk lore since Antiquity (of a kinder nature Norwegian tradition had
Huldras and a
wider diversity of 'trolls' than modern tourists would believe).
Vampires of the 'romantic / Victorian' type
à la Carmilla / Dracula (unharmed by sunlight, btw) appeared in Western European literature at by the mid-18th C. even if the
first' successful' one dates from 1816.
Voodoo
Zombies were by then mostly restricted to Haiti but a crazy explorer could have brought back a Voodoo witch-doctor from his travel oversea, just like another one brought back a lion (?) in 'Brotherhood of the Wolf' or drugs with 'Dr Jekyll & Mr Hyde' side effects in the French TV 'Bête du Gévaudan' -and then his mysterious 'exotic' wife could be a
Shambleau. Alternatively if one subscribes to the 'modern' (Resident evil, [rec]...) interpretation of
zombies as diseased persons, the plague could have
arrived with a ship, so one can play '
Pride and Prejudice and Zombies' in Georgian England.
Mountainous areas of 18th C. Europe were as backward and in winter as isolated as remote settlements in
Nouvelle France: hence the plot of
Le poil de la bête (a kind of Anthony Quinn's 'Battle of San Sebastian' with werewolves instead of half-breed
bandidos, set in late 17th C. French Canada) could be relocated there. As could the action of
Ginger Snaps Back,
Werewolf: the Beast among Us and of that movie (the title of which I forgot) set after the ACW and featuring cannibals; 'generic' ghouls such as produced by
Heresy,
Mantic and
Taban are perfect for totally degenerated inbred (and
kuru-afflicted?) villagers of Lovecraft's '
Lurking Fear' type.
Half-way between fantasy and weird science, what about complementing the
Phlogiston, the
Aether and the
animal magnetism with
orgone and the
Vril?
'Advanced' science and technology: while the first functional steam-powered carriage (
Cugnot's fardier) and boat (
Jouffroy's pyroscaphe) appeared late in the 18th C., steam engines were used since the beginning of the century to power pumps draining mines: thus
steam-powered vehicles could have appeared earlier -an 'enlightened' ruler may even have ordered a steam version of Da Vinci's tank!
Similarly hot air balloons and the
'Turtle' pocked submarine of the AWI could have be built far earlier in the century.
Da Vinci 'birdman' flying device was actually a directional parachute /
hang glider and could be used as a 'Jamesbondesque' device used by the hero as in
Assassin's Creed IIhttp://www.youtube.com/watch?feature=player_detailpage&v=-3RTx5fowAw#t=21s)

The old 'Wild Wild West' TV series offered other inspirational gadgets such as a primitive gramophone.
As for
weaponshttp://www.youtube.com/watch?gl=US&v=m-uj_t--tEEboth
Puckle's 'machine gun' and Philip V of Spain experimental musket were breech-loaders using pre-loaded cartridges; a 'handgun' version of the Puckle would have be equivalent to the Remington 1858, in heavier and more cumbersome.
The
Girandoni Air Rifle entered service in 1780, but implied no recent technological breakthrough, only individual 'audacity' and ingenuity in design, so could have be produced far earlier; the same for the
Ferguson rifle -Marshall de Saxe in his '
Rêveries' describes an advanced breech-loading mechanism for his 'amusette' very light cannon, infantry musket and cavalry carbine.
The secret of Byzantine 'Greek Fire' were lost in Europe, but naphta-based weapons were constantly in use in the East (from the Levant to China) since the Crusades: in the same way as rockets were historically 'imported' from India, a primitive
flame-thrower would not be unlikely.
Thus, even without the addition of 'quasi-steampunk' weird weaponry, major characters could be well equipped to face any threat in a 18th C. 'Empire of the Dead'.
But such 'advanced' weapons are to be kept few and far between, otherwise one would be merely playing VSF with figurines bearing wigs and tricornes.I confess that the weapons in the drawings of the original post look more 'steampunk' than 'lacepunk' to my eyes: for instance the repeating musket seems to be provided with a very 'modern', if weird, revolving magazine {NOT a revolting magazine ^-^} rather than with a 'period' cylinder like the Puckle gun; and imho this 'armored' version of the fardier is 'too much' for the 17th -18th C., even very 'enlightened' -and how does this monstrosity *turn*?Besides, oil lamps would look more 'enlightened' than candles:
For the really *daring*,
cavorite and then
liftwood could have already be discovered, allowing a
'Space 1745' campaign; if space travel is 'too much', then have cavorite and liftwood on a
yet-to-be-discovered small continent in the Pacific Ocean.

(
from)
Lacepulp / lacepunk games are already played by an active minority (
some 20 links: scroll down to the O1.04 post).
While a special
set of rules would promote the genre, a few good
miniatures would suffice and be far more effective.
Suitable rules already abound, and sets intended for a later 'Horse & Musket' period such as '
Chaos in Carpathia' can be used as they are to play