You can use a QR code to print on business cards. There are a ton of sites that allow you to create codes. You can google to see which ones offer the services you need (expires after download, etc)

Check out Gumroad.com and PayWithATweet.com - those types of tools should give you a good starting point to have a capture method before delivering a digital good.

As for the couponing / code system you reference, I know you can do it with Shopify and some of their digital delivery plugins - but it will require a fair amount of time to setup (12 hours)

I believe you should invest some more time to simplify the idea. Content or business cards, either way it's going to be a database building and lead generation activity for you. The question is, what value are you trying to communicate? Is it the premium content or the referral?

The online marketplace out there is already undergoing the wrath of paralysis-analysis; all due to availability of too much diverse quality content. How would you ensure that yours is a premium one?

As far as including a download link is concerned, that's not a big challenge and could be easily done by any technology enthusiast. Is there something big that you're trying to accomplish? Feel free to reach out with more clarity.

I believe this link will help you greatly: https://businesscard.bhybrid.com/en/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath