A: Annoying as this answer it, it really does depend. Some purchase orders (especially in the government contracting world) automatically become contracts once they are accepted and signed. If this is the other sides normal mode of operating it is not unheard of for them to be reluctant to accept a different contract in case it creates different or conflicting terms. At the end of the day there is nothing inherent in a PO that would mean it cannot serve as a binding contractual document, it just depends on the language in the PO.
A: Typically your options are going to be controlled by the SAAS Agreement or other contracts between you and the client. There should be a section in there called “Termination” or something similar.
Really, it would require a review of the contract to give more specific advice on this one.
A: So non-disclosure agreements will typically be enforceable for a reasonable time depending on the content of the information contained in the NDA. It will really depend on the specifics of the NDA and the information released to you. Most NDAs do allow you to discuss the matters with counsel so if you are concerned about any specific agreement it would probably be best to have them reviewed by an attorney.
A: Generally a fix term employment contract differs from a genera employment contract in that it has an end date. For example, at-will contracts continue until you are fired or quit, while a fixed term contract only continues until the term expires.
The main points to look at would be what they are classifying you as (employee vs contractor), the length of the term (so you know when the contract is up), and how to renew the contract or if there is an automatic renewal. It would also be good to double check the contract for termination clauses, as quitting may be more complicated under a fixed term contract.
Ultimately, as with all contract matters it’s probably best to reach out to an attorney to review the document to get more specific answers to your concerns.