Rules in Eire do not really support either homebuilding or any kind of US-experimental type system. This is why the majority of people building "interesting" aeroplanes in Ireland do so under supervision of the PFA or BMAA.
So, you really are limited, being practical here, to joining the PFA in Britain, and building something under their supervision. It gets worse I'm afraid, because the IAA are totally against any form of test flying being done in Irish airspace - even on Irish registered aeroplanes.
So, having built your aircraft, and done so under a British registration, you'll almost certainly have to trailer it North to somewhere like Newtonards for flight testing. Once it has it's UK Permit to Fly, the IAA will then however generally be quite happy to issue an Irish Flight Permit on the back of that.
Finally, the Velocity is a big complex aircraft to build - unless you are a timeserved engineering technician, or have built several other aeroplanes I'd not contemplate something of that complexity. Look at the PFA list and speak to other builders and pick something reasonably painless for a first build; on other words, something you might finish!
If it's not on the PFA list, or about to be (and take nobody's word on that except PFA Engineering), I'd not touch it - it will end in tears.
G