Are my startup costs determined by the date I filed and received my state & federal documents (2/25/19), or are they all costs incurred up to when my website went public?
Neither. Startup costs are those costs incurred before you were "officially open for business". That "Open" date is determined by you. It's perfectly possible for you to have been open for business on 1/1/2019 which has nothing what-so-ever to do with your document dates or website publishing date. But do check for dates in your state and fed documents. If those documents give an "effective date" then I would recommend you establish your "open" date on or after the effective date in any of those state or fed documents.
I know I can only deduct $5k this year and will amortize the balance over the next 15 years.
It's only worth it to you to claim the full $5K in that first year, if you actually have $5K of taxable business income after all other business deductions are taken. SO keep that in mind.
