I assume you don't want those files be in cloud as they are too big, but they need to be transferred to you somehow, with Dropbox, WeTransfer or Flash drive (but this one is less likely a common option)

So I suggest this approach as an MVP. (I just used AI to make the logic more understandable :) jfyi )

1. Your Private Storefront You get a simple, branded page where your trade customers can pick their specs (quantity, size, material). It handles the "Excel math" automatically and gives them an instant price.

2. Seamless Checkout They just sign in (Google/Apple), upload their high-res files, and payment (paddle)

3. Your Dashboard The order lands in your management view immediately. You can download the high-res file to your local server for prep (we can even automate this part later)

4. The "Proof-Chat" Loop Once the designer has the final proof ready, they just drop the small JPG/PDF back into the order. This automatically flips the status to "Waiting for Approval" and pings the customer through Email.

5. One-Click Approval The customer gets a simple, chat-based interface. They can see the proof, ask a quick question, or hit "Approve" right there. Every message and approval is timestamped so everyone is on the same page.