If you qualify as a US resident under Substantial Presence, then residency begins the first day of the tax year. If you qualify as a US residence under the Green Card, then it's your first day of the year as a permanent lawful residence. If you qualify for both then take the earliest date.
It is the timing of the receipt of income, not when you earned it. If you earned the money while you were a non resident but received it as a resident then that it's taxable as a resident.
Cannot use the HOH filing status.
Married residents of Canada and Mexico or South Korea or married US nationals can file as single if they lived apart from their spouse for 6 months.
Standard deduction is not allowed, only itemized and must match the period being reported.