Validation is only requested when you start your first itch payout. But, it’s likely to fail for unknown reasons (see rest of this thread). Good luck.
I would advise using PayPal/Stripe payouts.
Not according to the HMRC website:
VAT accounting options for UK businesses supplying digital services to consumers in the EU
The place of supply will be where the consumer is located. You must either:
- register for the Non-Union VAT MOSS scheme in an EU member state
- register for VAT in each EU member state where you supply digital services to consumers