Best practices for Anonymous Crypto Payment System With User Tracking and Minimal Gas Fee

Hello! I'm looking to implement a crypto payment system where users can deposit funds without logging in—ideally through a simple QR code scan or by pasting a wallet address. However, I still need a way to track each user and monitor their total deposits. The main requirements are: 1. Users deposit anonymously without requiring login. 2. The system needs to associate each deposit with a specific user ID for tracking purposes. 3. I want to know how much each user has deposited over time. 4. Ideally, I’d like to minimize gas fees and avoid dust deposits.

Questions: 1. Has anyone implemented a similar system or found ways to make anonymous deposits work while tracking users reliably? 2. When scanning the QR code in MetaMask, the metadata field appears empty. Has anyone encountered this issue, and is there a workaround to pass data reliably with the QR code? 3. Would using smart contracts be feasible in this context? If so, how could I reduce gas fees and avoid creating dust amounts? 4. Alternatively, is there a way to generate unique deposit addresses for each user and avoid dust completely?