How are feudal contracts negotiated and what would they cover and what would the terms be like generally? What about renegotiations of the contract?

See here and here for previous writings about the feudal contract.

Feudal contracts weren’t frequently negotiated, because tradition was considered incredibly important and breaking the traditional terms of the contract was frowned upon in the extreme, and innovations like scutage weren’t always thought well of either. Generally, if they had to be changed, it was usually done by trying to find some sort of ancient precedent, or if that couldn’t be done, by inventing one out of whole cloth and doctoring the records. 

They varied tremendously, but usually they involved a bilateral exchange: the liege lord offers rights over a certain piece of land (not an absolute right to the land itself, but that’s a bit tricky given the difference between pre- and post-enlightenment conceptions of property rights) in exchange for stuff. It usually included military service (hence the practice of dividing fiefdoms into knight’s fees), although if a fiefdom was given to the church this was usually commuted, but it could also include various traditional forms of taxes (so many pheasants or so many butts of wine, etc.) or personal service (holding someone’s stirrup when they came to town, being their cupbearer, etc.).