My endo want to do whole body scan with i-123 before having me go on rai for pap thyroid cancer. shouldn't he do the rai first &whole body scan later?

Depends: It sounds like you are having rai now because you didn't do it initially, rather than having it to treat recurrent disease. It is reasonable to do the scan first to assess how much thyroid tissue is left in your neck, and whether there is evidence of disease elsewhere in your body. The dose of rai would then be adjusted by the findings.

It is done sometimes: In some situations, a diagnostic scan with I 123 is performed before a treatment with high dose Radiodine, to identify the amount of disease burden and to help with dosing of the radiodine treatment.