What information about the originator does the processing server know about (originator IP, wallet address, amount available to spend, etc.).

The incoming server knows all the information about the originator, however it doesn't record any of it as verified by reading the source on github. The outgoing server knows nothing about the originator, it only knows about the incoming server which forwarded the transaction. This is part of how we disconnect originator from receiver and why we setup 2 servers and not just one.

What is the potential that the decrypted data can be viewed by the server operator and/or logged by the server operator?.

High potential. This is why each server operator only transacts within their trusted cluster and each cluster is publicly listed with user ratings. The Official Nav Coin cluster guarantees that we run the exact code which is available on our public github which can be verified not to be recording any of the encrypted data. If you don't trust us, configure your wallet to use a cluster whose operator you do trust. If you don't trust any operators, then feel free to setup your own private cluster that only you use.

What is the size of the preloaded pool of NAVcoins?

We have 50k loaded on each of our 4 outgoing servers. This amount can be whatever you like really, but it should be at least the size you set your maximum transaction amount to be.