For GDPR Article 17 "Right of Erasure" may require you to have a mechanism to delete all forum posts and private messages for a particular user.
I don't think "Right of Erasure" would cover articles written by someone in the unlikely event of an author requesting erasure.
"Right of Erasure" does not trump the legal requirement to keep financial records for the legally mandated time period
If Redgate haven't done so already it is wise to get advice from legal.
Article 20 "Right to data portability" is an interesting one. It doesn't limit its scope but I think historically it re-enforces consumers rights to swap energy suppliers, broadband/mobile providers and now banking providers. In the context of SQLServerCentral it could be a mechanism to download a subscriber's profile by that subscriber.
Maybe. Our business is providing answers to people. It's possible an entity could get a right of erasure, but I doubt it for the things we share. We'd want a legal decision to the contrary.
For Article 20, the profile is a good example where we might need to provide that for someone, though I doubt we'd get a request. We keep fairly little information here that isn't public.