Teaser: Code works, some kind of countersign, maybe even a chance for some subtle humour or veiled references.
Used to work in logistics, once upon a time. A truck driver knows what's on their truck. It's a matter of law and safety. They need to know if it requires special precautions and they'll check it's loaded properly themselves 'cause it's them that'll end up in trouble if it starts shifting. That being the case there's no need for a conveyance on the trailer. The trailer can be a specially adapted prisioner transport trailer. They get loaded somewhere secure, they get off somewhere secure. The trailer could be switched for a dummy trailer at Site-76. Why waste space by filling it with an engine and wheels? Where would the toilet go!? Do you forsee the bus driving out, Knightrider-style? Maybe I'm missing something?
Act 1: Fair enough, it's your script. If they're Foundation-issue, consider who else is issued them, what they're used for.
Act 2: Sounds like a difference of opinion, again; your script. As for the cartwheel, etc. - I picture the disarm happening with the sarkite at approximately shoulder-height and Yoo nearly at ground level sliding low, one foot leading. I get the impression you're picturing it higher and with Yoo diving head-first so they are head to foot with each other. Maybe just a difference of visualisation. Remember that the sarkite is jumping through a door so the maximum height of his jump is restricted.
Act 3: Suggestion - add cuts to imagery from the text of SCP-140. Sarkic rituals, massed battles won and lost, abominations abominating.
Act 4: The MTF have spent months or years training for this. They don't need to be told they might die, they know, bone deep. I think a business-like speech and them just getting on with it would contrast nicely with the horrors they then face. Maybe have a small background event of a newbie questioning a veteran: "Is this going to be bad, Corp?" "Oh yeah, kid; it's going to be bad."
Act 5: Let's see it. Might be better to space any tension-building over a large part of the act as cutaways while the protagonists dialogue plays over. Saves just springing it at the last minute.
Speaking voices: Yoo and Mahto are pretty distinct. Grey and Kliks are maybe more similar to each other. Have you considered making Kliks smoother, more charming and pleasant, on the surface? He seems to have got ahead and if he had that executive slickness that might blend well. Maybe make Grey more rough by comparison?