Is a ransom due from me for performing ihram from inside Makkah or for staying in Muzdalifah only until midnight? And do I have to perform the Farewell Tawaf if I will return to Jeddah while continuing to come to Makkah for work?

If you performed 'Umrah during the months of Hajj and then performed Hajj in the same year, without traveling a distance that permits shortening prayers between them, then you are considered a mutamatti' (one performing Hajj Tamattu') and the dam at-tamattu' (sacrifice for Tamattu') is obligatory upon you, even if you did not intend Tamattu'. And your ihram from Makkah is valid.

If you are a mutamatti', you must slaughter a sacrificial animal in Makkah. If you are unable to do so, then you must fast for ten days: three during Hajj and seven upon returning. If you miss fasting them during Hajj, then fast the ten days wherever you are.

Your departure from Muzdalifah after midnight is valid and nothing is incumbent upon you. However, if it was before midnight, then a sacrifice is due. You must perform the Farewell Tawaf upon leaving Makkah, even if your departure is to Jeddah.