PHP Script

Good brief. Below is a concrete, modern approach tying together the ideas from @darkagn and @khess so the PayPal gating, role redirects, emailing and theming all behave reliably and securely.

For payment gating: use a server-to-server notification from the payment provider to create or flag a "paid" record in your DB, then allow registration or send a one-time activation link. An alternative is to sell redeemable license codes (one code = one subscription level) that the buyer redeems during registration. In either case record: transaction id, buyer email, subscription_level (1–5), start/end dates and status so you can handle refunds or expiries later.

Permissions and redirects: store a numeric subscription_level in users. Keep a lookup table mapping levels to spreadsheet IDs or protected paths. After login set the level in the server session and always check it server-side before serving a file or redirecting. Never expose direct file URLs; serve spreadsheets from outside the webroot or stream them through a checked PHP endpoint so unauthorized requests fail.

Email, password and automation: use an SMTP-capable mailer (with TLS) for reliable delivery. Send purchase receipts, registration confirmations and password-reset links. Implement password resets with single-use, time-limited tokens (store token hashes, expire quickly) and rate-limit requests. Use password_hash/password_verify (or equivalent modern hashing) and parameterized queries (PDO or mysqli prepared statements).

Integration and ops: separate presentation (header/footer templates) from logic, use Composer to manage libraries, test flows in the payment sandbox, and log IPN/webhook events for troubleshooting. Vet any third-party scripts you find (as @khess suggested) and follow @darkagn’s lead on using an ACL-style approach—just ensure the ACL stores roles and resources in the DB so it stays flexible.