Not sure you'll be able to. Many of the restaurants at Disney Springs have there own reservation systems outside of MDE, like Paddlefish and Planet Hollywood both use OpenTable. I don't believe those types of reservations can be linked to MDE.
Not weird, standard for most the DS third party restaurants. They only give Disney so many and the rest they hold back. Always been better to reserve on your own direct.
No. You can cancel right up to the time of your reservation without a penalty if you make it directly with the restaurant. Pretty sure even a no show isn't penalized although I don't suggest people do it.