Is it permissible to delay Tawaf Al-Ifadah along with Tawaf Al-Wada' and return to Madinah due to congestion, then come back to Makkah to perform the Tawaf, and what is incumbent upon one who masturbated before completing the Tawaf?

There is no blame upon you for what you did by following the fatwa of the aforementioned shaykh, and nothing is required of you, Allah willing. One who intends to travel from Mecca before completing the rites of Hajj is not obligated to perform the farewell circumambulation (Tawaf al-Wada'). As long as you returned and performed the circumambulation of overflowing (Tawaf al-Ifadah), your ritual (nusuk) is complete. As for your masturbation before the second partial release from consecration (Tahallul al-Thani), it is forbidden (haram), and it requires an expiatory offering (fidyah) along with sincere repentance (tawbah nasuh).