So I'm planning to run a one shot adventure at a local game store using 5th level pregen'd characters.  I've got the encounters all set (all in the Medium range, with a few easy, and one deadly if they don't track down the couple of OP magic items first) but I'm struggling on the pregen character front.

I found this link: https://dnd.wizards.com/articles/features/character_sheets

How do these guys stack up with what you would find typically in a campaign at 5th level.  I'm looking at the encounters and I'm already a little worried that widdling down a Vampire Spawn with 82 HP is going to be, well, brutal to a party with at best +1 weapons.  And she's part of a "medium" encounter (with two lesser vampires with her, CR1 each)

I tend to focus on story over combat so I'm worried that I'm not going to hit a sweet spot of "too hard" vs "too easy" when the players draw steel.

Sounds like it might be medium for a party of 4, but a party of 6 will steamroll the encounter.  use the ddb encounter generator, or even KFC.  Also, don't be afraid to tailor the pregens for the encounter

Well longer story:

I'm prepping to run Ravenloft (I9) as a one shot event at a convention in a 4 hour time slot. I want to focus on the story more than the combat but I want to get 2-4 good fights in during the session as the players make their way through the major plot beats. I haven't run anything 5th edition but I've been running games since the Red Box so I'm mostly just getting my head around ~this~ edition.

I put in 5 players at level 5 for the encounter generator and it kicked out "Medium" as the challenge. I also want to cap the play group at 5 for a few reasons: One is to learn the rules with less players. Another is to have more players NEXT week to run the same event, same module, by pulling people I couldn't fit this week. I also think that if we go past 5 we lose any chance at party banter in the shuffle and combat can DRAGGG...

So the tool says I'm in the medium range but I still can't shake a bad gut feeling that they're going to be undergeared. In previous editions you had a "by this level you should have this much money" going on and could use that to go "shopping". But they seem to have taken that out...

Is gear just not a factor as much now?

5E is considered "low magic."   So, characters don't have the amount of magic items compared to earlier editions.  DMG Chapter 7, Magic Items, Magic item rarity, has a chart with a recommended rarity availability per level.  DMG Chapter 1, Tiers of play, gives a basic idea of the power level at each tier  - including a general idea of how magic impacts their adventures.  Xanathar's Guide, at the end of Chapter 2 is a section called Awarding Magic Items, and it goes into more detail.

Hmmm.... I'll review it.

My biggest worry right now as I prep is the number of things that are resistant (or even immune) to non-magical damage.  I can totally fudge the rolls as needed if the party is getting hammered, or forget about the resistance, or some other tweek, I just want to be minimize how often I do that, if at all.  And I don't want to make some modifications in one area just because I didn't give enough ooomph in another.

Someone more experienced correct me if I'm wrong, but to address the magic resistance you don't need a +1 wep in this edition, so you can look to things like Moontouched weapons and other non damage enchantments to avoid skewing the game balance.

Quote from Noksa >>

Someone more experienced correct me if I'm wrong, but to address the magic resistance you don't need a +1 wep in this edition, so you can look to things like Moontouched weapons and other non damage enchantments to avoid skewing the game balance.

 Hmm.... I was thinking about doing something like that with the party:

Have the priest bless their weapons with a spell that would last until sunrise.  It would give them an incentive to go forth and free Barovia without necessarily feeling like an artificial speed up.  And it would set the stage that this is a single epic night of glory, not a long campaign against the darkness.