The short answer
Keep six groups of information: item and seller, order source, current stage, paid and remaining amounts, key dates, and the next action. Add the original screenshot or link so the seller’s wording remains recoverable.
The six core groups
Record the item and seller; the order or announcement source; the current stage; deposit, balance or full-payment amount; opening, deadline and estimated dates; and the next action such as paying, checking an update or confirming receipt.
Why spreadsheets become expensive to maintain
A spreadsheet can work, but you must design the fields and states yourself. Information is still scattered across messages, listings, order pages and screenshots, so every entry requires finding, copying and maintaining it. Reminders are usually a separate system.
Use a low-maintenance routine
Create the record on purchase day. When the seller publishes a new window, update only the date and next action. Move the stage after payment and archive only after receipt. Screenshot OCR should produce candidates for confirmation, never silently turn recognition into transaction truth.
A quick completeness test
Close the original order page and ask: where did I buy it, what must I do next, and when is the last or next useful time to act? If one answer is missing, the record is incomplete.
What a tracking tool cannot solve
A tracking tool cannot supply information the seller never published, verify actual production progress, monitor social pages automatically or guarantee notification delivery. Update the record when the seller changes the plan.