1. If I had some personal used days for my rental but then I rented it for a long term, I didn't used it 100% for business for the first year but it was not my residence either, can I amortize those costs in the same way you described in your answer?
When it comes to long term rental, what the property was used for before you converted it to a rental, does not matter and does not count for anything.
2. if I rented my house as a vacation home and it is my residence, can I amortize those costs in the same way you described in your answer?
I'm finding it hard to follow you here. I think it's the way you're wording things here. You can't rent out property "as a vacation home". But you most certainly can rent out all or a portion of your vacation home to someone either long term or short term. A house can not be both a vacation home, a rental and a primary residence at the same time. Perhaps you rented out a room in your primary residence for a defined period of time? Maybe you rented out a portion of your vacation home for a defined period of time? There are criteria in IRS Pub 527 and define short term rental, long term rental, and a section that covers renting out a portion of your primary residence for either long or short term.
Since your post is an add-on to an existing thread, it would be best if you would start your own thread giving the specifics of your particular situation, so your questions can be understood in "your" context.
