Thanks a lot for this mate and sorry for my late reply.
Would having non-paying nodes forward transactions even be possible?
Sure. Thanks for all the good questions! Quality discourse does everyone a favour.
A non-paying node would have no payment to submit to the mesh, and thus there would be no basis for it to be included in the transaction.
Snipped most of the convo but wanted to thank you both, this is great info and helpful for everyone to understand how Xmixers and transactions work.