Is it doable solely within the creation kit, or would individual skins need to be created for each creature to match the "ghostly" effect similar to the wolf familiar? I'm capable of the former, not the latter, unfortunately. I've looked around a bit within the spell and spell effect, but I'm not positive either way. I'm leaning towards needing an individual skin. If that's the case, what would be a good workaround or compromise?

The idea is to create scaled familiar spells. Apprentice would be a sabrecat, Adept would be a bear, and so on...though I'm not sure what I would do after that (Expert or Master).

You can do it solely with the Creation Kit. The ghost effect is actually applied to the actor by a script, you should see the one I'm talking about attached to the default wolf familiar.

I'm looking through several of the screens, but anywhere there is a script section, it is empty (no entries). Where should I be looking?

If I'm looking at this correctly, seems like the "script" is shown as a magic effect/spell in and of itself (abfamiliarvisuals and FamiliarVisuals, respectively). As stated, it is applied to the default familiar spell, so I should just have to, essentially, change the creature that is summoned, correct?

...Huh. I could have sworn this applied to the wolf familiar too...

Apparently the script I was thinking of was the one attached to a horse used in one of the random encounters. The one this guy uses: http://uesp.net/wiki/Skyrim:Headless_Horseman

It's called WE-something-12, I don't have it right in front of me at the moment. That horse should have a script attached that applies the ghost effect. The actual shader itself is an ability/magic effect, but the death effects and such I believe are controlled by the script.

Might be simpler for you to just toss the familiar's ability on your new creature and see what it does. I've never tried, but it should work. The familiar's mesh and texture are just a regular wolf I believe. It's all in that shader.

It worked!

I made a Conjure Spider Familiar spell (complete with spell tome), that summons a Giant Frostbite Spider. It has the blue, transparent glow, just like the wolf familiar! The only thing I didn't do is set the correct spell level/cost. I thought about making it an apprentice level spell (it's a level 14 creature), with the same cost as a flame atronach.

I'll look into what's going on with the Headless Horseman. I know the effect you're talking about, and I don't see that on my spider familiar, but I didn't see anything specific with the regular wolf familiar spell, either (in the CK).

Edit: The FamiliarVisual effect has the same blue "smokey" look that the regular familiar spell has, not just the blue skin/texture color. Oddly enough, you can see more of the spider's regular colors as well (whereas on the default familiar, he's completely transparent, save for the FamiliarVisual effect). This "look" seems to work well enough.

Now, I just have to create a Sabercat for the Adept level spell, a bear for the expert level spell, and I was thinking a mammoth for the master spell, haha.

Hmmm...can't seem to change the spell level from Novice to Apprentice. Seems like it should be easy, but I can't figure out which setting to change.

I also can't figure out how to Auto-Calc the cost for the spell, but at least I can manually set that if need be.

The casting perk controls what perk you need to reduce the cost. I believe that also determines the level of the spell, but I'm going off of memory here (and mine admittedly is not that good, lol). The default familiar uses ConjurationNovice00, set it to ConjurationApprentice25 and see if that does it.

Uncheck then re-check Auto-Calculate. It should give you the new cost.