<gulp>€400k for that level of work in Dublin looks like a pretty tight budget to me, particularly if you are going for a high spec.
2019 RIAI Consumer Cost Guidelines (ex vat): Extension - €1,900 to €2,300 per sqm / Renovation - €1,800 to €2,000 per sqm.
So, €460k to €530k (ex vat) for your project.
Thanks, I think I saw numbers I used based on some other folks experiences, but RIAI sounds more reliable. Might be better off just knocking it all and starting again.
Big picture, I guess we can afford it, or we can shrink the project.