When considering a specific teaching position, it is important for you to determine which are the negotiable versus non-negotiable factors of your contract. If curious about the finer details of the position, questions should be carefully placed in terms of timing and of whom they are asked. For example, asking a recruiter about whether or not there are windows in the classrooms is misplaced timing and is asked of the wrong person. Questions should be categorized as need to know (needing answers before you sign the contract) versus curiosity (you would like answers if possible after the contract is signed), and asked accordingly.
You will not get everything you want in a contract. List the items that are important to you. Reflect upon what you want in your contract and what you consider to be acceptable. You will most likely get something in between. Keep in mind, however, that the more you attempt to negotiate, the less desirable you are as a candidate.