1. Can I put two print on demand items side by side and have the viewer choose one by clicking it?
If its rewards after sharing that you want to print then you can, but that's all on your end.
2.Can the click target a separate/different landing page for each item?
You can do this as multiple campaigns, but they are in no way linked to your userbase (could be a cool feature for later on -> shared users across campaigns)
3. Can I have a landing page, with more info about the item, and offer a coupon if they opt-in to list?
Yes, it can be in the welcome message shown on page after signed up or sent via email. This is also true after [x] signups via triggered rewards (they’d have to enter the code we do not generate it)
4. Can a coupon be one time use?
What you offer is under your control - where you create the coupon is where it's use would be restricted
5. Can signups be limited to single signup from a single IP address?
We can think of a hard limit but this is difficult for places such as universities, airports or coffee shops and public places who provide internet to the masses. People are flagged automatically in the fraud center but not limited (unless you ban the IP)