When a masbuq joins Salah in four Rakah and stands up after the Imam says 'salaam', does he say the takbeer before recitation of Surah Fatiha (of 1st Rakah)?

The Masbooq should recite one Takbeer whilst rising from the sitting to the Qiyaam position. Thereafter, he must recite the Thanaa, Ta'awwuz, Tasmiyah, etc. There is no need to recite a new Takbeer whilst standing.

In order for us to answer the second part of your question, we need more clarification. We need to know whether your question is regarding a Masbooq in a two, three or four Rakaat Salaat.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai