1. If you are eligible for the FEIE, you can use the foreign residence deduction, but in practice it is not very effective. If this had a big impact, either you’re paying your loved one a lot of rent or you’re not calculating the deduction correctly. Your accommodation costs must exceed 16% of the FEIE ceiling to be deductible. So if you pay your parent around 57,000 baht per year or more, you can deduct…although this is capped at 30% of the FEIE limit.
2. Maybe. Maybe not. It will depend. First, you cannot stack deductions and claim a deduction twice for the same expense. Second, there are specific rules relating to home office expenses. But conceptually Form 8829 can be used to claim expenses for business use of your home and should be filed with Schedule C if I recall correctly. …but I think the area should be used exclusively for professional purposes, not a mix of personal and professional use.. but I have to admit that I’m not really aware of the details about it.. Read the Form 8829 and its instructions.
3. Which line are you referring to. Assuming you are applying as a bona fide resident, your residency start date would be 2011 or later if you did not become a bona fide resident upon arrival. For home deductions, I don’t think they ask when you established the home…unless my memory is faulty –
4. It probably doesn’t matter, these questions are there to validate your eligibility, and given the time you spent on them, it probably has no consequence. But that said, how did you file in previous years? I would suggest doing the same.