Welcome to the board. Yes you can convert an ICAO PPL to an EASA PPL. Any ATO (Approved Training Organisation) should be able to do this for you. As you mentioned, if could be done with AFTA in Cork or NFC in Weston. Perhaps anyone who has done it can share their experience here.
To answer your questions!
4) There is a Decathalon at Cork in AFTA. NFC have some Aerobatic C152's. Outside of that, anyone who wants to do aerobatics has either joined an existing group, formed a new group or bought an aerobatic aircraft outright.
5) Yes AFTA in Cork have some Aeros instructors. There are also some display pilots in the country who do some ad-hoc instruction but not full time.
We used to run FlyingInIreland Magazine for 10 years, this was a printed publication but we ceased publication in 2015. There are no other magazines at present as Ireland is a very small market and can't sustain it. You'll find a list of Irish aviation organisations here - https://flyinginireland.com/links/
, the top section lists the flying clubs.
Hope this helps!