Would you offer some insights on helping me find instruments already field tested for validity and reliability? Anyone know where I can find surveys I can obtain permission to modify.
You need to look at the surveys used by the National Center of Education Statistics for their teacher retention studies. If you go here you will find their surveys used for teachers who were beginning teaching as well as their follow-up surveys:
If you are looking for different instruments you might find it helpful to look at the English teacher labour market work of John Howson, at DataforEducation.info (https://about.me/john.howson).
I used the Beginning Teacher Longitudinal Study for my dissertation. It requires a restricted use license, but contains a wealth of data. The new BTLS completed in 2017, but I am not sure if the NCES has it available for use.