1) Is it permissible to move any body part during namaz or to stop ziker then continue?

2) I said tashahud in 3rd rakat of Isha namaz and realized for 4th rakat and continued 4th rakat is namaz proper?

1) While you are reciting, moving is not allowed except when a person standing for next rakat and says Be Hawlillaj wa Quwwatehi aqoomo wa Aqud.

2) If you recited tashahud in third rakat, namaz is correct but after the completion of the prayer do sajda e Sahv for and additional Tashahud.