A1 - Where you buy isn't relevant, as I've already explained to you - Irish Revenue want you to pay them the VAT that is relevant to them, which is Irish VAT. If a Ukrainian supplier charges you Irish VAT (which I find implausible to be honest) then you are entitled to claim it on your return. Generally though a non-EU trader won't/shouldn't charge you VAT, but you are obliged to pay the VAT at point of entry and account for it on your VAT return.
A2 - if you have been charged more VAT than you have taken in then you are due a repayment from Revenue of the difference.