3. Registering as a company makes no difference since I won't have any taxable sales I can write it off against.
Sales, no.
However since you are mining for profit - and business profits are taxed - that is where write offs come in. In the US at least, the miners are Capital Equipment required for the business. In fact the IRS views them the same as any other computer or data server so they are write offs along with any import duties.