1. All of those that I cannot currently rent that I own and am listing on the market
2. That would be a spectacular feature if you could include it of course if it came down to it as much as the game can operate in DEC the better IMO.
3. Not sure but I would dump the remainder of any cards I have not already rented out on that kind of market, so whatever I would acquire from then on (at the creation of the system) that does not rent out the old way.
4. DEC as much as possible would be ideal-less hassle plus another sink 😁

These are some fabulous ideas. I think a hybrid of the new "pile 'em up and get what you can" massive bulk rental option you introduced and then maybe for more premium cards that people would want to hold back to rent for more the older individual listings may be the better way to go.