UK, Ireland / Bank transfer from Poland to UK - do I need only IBAN number or SWIFT one as well? [8]

You need both, IBAN and SWIFT.

Also, I use Xendpay.com for transfers between Poland and France, as far as I know they can transfer your money to UK as well,.

USA, Canada / Transfer of funds between Poland and Canada [5]

An FX company RationalFX can transfer your money to Canada for free, check their website.