I applied 6 years ago so things may have changed. Link may help you
https://www.agriland.ie/farming-news/apply-herd-flock-number/I requested the application form from agriculture food and marine, I’m close to Cavan so just called in. Sent the form in and the Regional vet arrange a visit to see my set up. Critical points being the amount of grazing for the number of lambs/sheep. Water supply. Shelter from severe weather (hedging, walls or field shelter etc.) Separate area and shelter to isolate a sick animal. I use 2 acres for 6 lambs but have another 2 acres that a lad takes hay off. This was more than satisfactory for the vet.
Being a hobby I did not get involved in tax, schemes, etc. The paper work for movements and records are simple enough and a quick phone call to AF&M will clarify any query. Once issued with a flock number I ordered the ear tags from
http://www.mullinahonecoop.ie/sheeporder.aspxI re read your post... I believe if you rent land, on a contract, you can apply for a flock number to keep your sheep there. Quick phone call to AF&M will confirm it.