Why are you lowering Corruption? Is there a Problem when it is high?
They stop having hopes and dreams, which can complicate quests. Also, flavor reasons. I like my girls kinky but not overly perverted/corrupted.
is there a way to hire a crew for your workshop. I mean actual employees like the factory workers at the plant.
You can free your slaves, elevating them to servant status, and give them allowances.
Whats the point of Fort Sera? I finish the Missions, but i cant recruit the Soldiers?
They increase your MC/House's power value. Institutions you can take control of like Fort Sera, The Catholic Church, and Odensport/Warrior's Hall add a portion of their power values to yours. There's influence gain and even money though that is on the lower end in income flow.
As for what power value does, not much for now. It adds to intimidation checks and others like it.
Where can i find the Savefiles?
If you have pressed the saved to disk option, it is in wherever your download is set to.
For example, I have mine set to the default Downloads folder so they are saved here.