No I think the CAO is completely different to what I've heard about UCAS to be honest. You are not even known by your name in the system, but your number. There is no personal statement. You must put your choices in GENUINE order of preference, not what you think you're capable of. This is because when the results come out, they take your grades and see if you're entitled to your first place, if yes all of your other choices are immediately struck off your list, if not they move on to your second choice and so on. So if you find you're more partial to your 3rd choice but you get your first, you'll never be offered that choice. You cannot track your choices, nor will any unis contact you since they're not in the frame until results come out. You have several times where you can re-order your courses or change them etc. though so no need to worry. DO NOT APPLY to the CAO online in the last few days of January, every year loads of muppets do this and the whole thing crashes and the poor pets don't get their applications through and have to pay double for the late application. So be on time! The structure may seem cold and unfriendly but it really is the most efficient way to deal with it, it might not work in a much bigger system such as UCAS though.
The CAO determine the points for each course. It works by supply and demand. This is why Medicine and Law have consistently really high points and why science, maths, nursing and computer science have average points. They're not as popular with such limited places. An extremely small percentage of Leaving Cert students get maximum points (600), I'm pretty sure it's less than 2%. So perhaps the Irish students who get 580 (ie. TCD's current Medicine points) would be 5% or less. This is a lot less than get maximum scores in the A-Level system and is the cause really of a lot of A-Level students not getting into Irish courses- it's extremely hard to compare the two anyway. They are not being deliberately unfiar and TCD in particular leaves a lot of places open for non-Irish applicants and has a massive amount of Internationsl students.
You are currently entitled to free fees (tuition fees being debated- there IS a registration fee of €1.5k though). Student loans and credit cards DO exist but it's not so much part of the student culture because of free fees. Accom wouldn't be as expensive as a few years ago but it's still a rip-off. Consider living 15 minutes or so away in an area with great transport links (although transport's a joke except for the minority). The cost of living is high though and since you're looking for medicine you won't really be able to get a part-time job.
cao.ie- you can order the CAO handbook from there. boards.ie is an Irish forum, under the sub-heading Edu(cation) you'll find the Leaving Cert forum (full of CAO applicants, although Irish), and a forum for each uni. Most will have threads for FAQ's containing links to older helpful threads that should answer a lot of your questions. Qualifax.ie has every course in Ireland and lists points etc. tcd.ie ucd.ie should have sections for UK students- both have their prospectus online. Good luck! I know lots about Trinity but not about how to apply through anything other than internal CAO tbh. And the HPAT is after my time.