Does an export include everything a service knows about me?
It includes what they classify as your data, which is narrower than what they hold. Derived profiles, inference scores and internal logs are commonly excluded. The gap is legal rather than technical, so the practical move is to compare the export against what the interface shows and note what is missing.
Is clicking delete enough?
It starts a process with a retention window, typically 30 days, during which recovery is possible and so is a breach. Export first, then delete, then check back later that the account is actually gone rather than merely hidden.
I want to share part of my archive publicly.
Strip metadata from images, search the text for names, addresses and tokens, and read the result once as a stranger would. Automated redaction misses context: a date and a place together can identify someone when neither does alone.