KIT SPEC — one page, written BEFORE you open anything.
Fill it in, delete what does not apply, keep OPEN QUESTIONS honest.

KIT: <name>
TARGET: <engine version, renderer features you rely on>
THEME: <one sentence — what a buyer would actually search for>

GRID
  base module              <cm>
  sub-modules              <cm>
  vertical module          <cm>
  grid owner               <corners | walls>   <- decide this in writing
  pivot convention         <...>
  snaps on default grid?   <yes/no>            <- say this in the store listing

TEXEL DENSITY
  target                   <px/m>
  exceptions               <which pieces, and why>

TRIM SHEETS
  sheet 1                  <material family>  <resolution>
  sheet 2                  <material family>  <resolution>
  drawn layout             <link to the sketch — draw it before authoring>

ASSET LIST  (sort by how often a piece appears, not by type)
  structural (20+ uses)    <count>   trim only, tightest polycount
  character  (3-8 uses)    <count>   trim + small unique atlas
  hero       (1-2 uses)    <count>   unique set, generous budget

BUDGETS
  triangle ceiling, structural piece   <n>
  LOD count                            <n>
  collision                            <simple | per-piece | hull>
  total texture memory target          <MB>

DELIVERABLE
  formats                  <UE, FBX, glTF...>   <- more formats = higher Fab
                                                  Limited-Time Free payout tier
  demo level?              <yes/no>
  documentation            <what the buyer actually gets>

OPEN QUESTIONS
  <everything you are tempted to hand-wave goes here, visibly.
   Resolve each one before it becomes a refit.>

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From the Shipping Kits series: vitchalany.com/articles/