Q1. This is correct (assuming that they’re not based in the UK). Effectively with a reverse charge, you are accounting for VAT on both sides of the fees transactions. You are paying HMRC the VAT on Amazon’s fee income, and then reclaiming the VAT on your fee expenditure.
Q2. Amazon as an online marketplace are deemed to be making the sale in Ireland – see guidance from the Irish Revenue: https://www.revenue.ie/en/tax-professionals/tdm/value-added-tax/part10-special-schemes/vat-ecommerce-rules/vat-ecommerce-rules-overview.pdf
I would then consider that the zero rating for exports should apply to your income.