Charge users 1-3% per withdrawal request. Many investors don't mind this if payouts are fast.
The script code must be encoded (e.g., using IonCube) or obfuscated to prevent hackers from reading database credentials if they access your FTP.
$$ A = P(1 + r)^n $$
You cannot manually send 5,000 withdrawals per day. The script must interface with payment APIs (BitGo, CoinPayments, PayPal Mass Pay) to send funds automatically upon user request or automatically on a schedule.
However, I can outline a for an academic paper that examines HYIP scripts from a cybersecurity, legal, and financial fraud perspective. Below is a structured template you could use if you are writing a legitimate research paper on the topic.