I'm starting to think about my next brew, and I'm leaning toward Yoopers Oatmeal Stout.
It calls for Wyeast 1335, which will be my first time using liquid yeast.
I scale my batches to 3.5 gallons, and I'm wondering, given the smaller batch size, is it still good practice to make a starter? Or will the yeast count be sufficient straight from the smack pack?
You've got about 100 billion cells in your smack pack. Depending on ester and other "growth" flavors you would like in your beer, the calculator flars gives is great - just plug it in. The "standard" pitching rate for ales that you see there - literally .75 millions cells per ml of wort per deg. Plato - is a good benchmark.
But, you can go a bit lower to encourage esters development; you risk higher lag time and possible infection. It's common for breweries to tweak their ale pitching rates a bit lower than the "standard," for just this reason - a fine tuning of ester content.
A bit higher, and you "clean" up your beer's yeast taste contribution. Here, relatively speaking, esters development is less, though fusel alcohols are encouraged, particularly if your ferment runs to the hotter side of its range. If significantly overpitched, not only are these things more pronounced, but you can end up with flavors contributed by autolysis - the breakdown of yeast tissue, causing brothy, meaty flavor.
Where I worked, both were done, for their respective purposes. Ales were often underpitched, lagers were often overpitched to tame sulfur pickup and expression, etc.
To keep it simple, so long as you're not brewing a high-gravity brew, you're fine with just the smack pack, presuming it's fresh. "Fresh" is really important, because viability can drop off considerably for aged or improperly stored smack packs. In which case, you'd have to either lower your viability input and increase the amount you'd need, or find some fresh yeast and go ahead.