To answer your first question, of course they wouldn't be telling people to go to the hospital, it would only affect more people. The problem is their current plan is you're told to ring your GP (doctor). Your doctor will then tell you to contact the national health number, who, when you ring, will tell you to contact your GP. If you say you have, they'll pretty much say "sure, just self-isolate for a few days, it could be a flu" even if you're dying. Look it up on /r/ireland, while it may be anecdotal I have no doubt in my mind it's true, considering how woefully shit the public health service in Ireland is.
To put some perspective on things, the country for the past few years has been facing a massive health service crisis. Even in the past year before the coronavirus waiting times in the Accident & Emergency department can be up to twelve hours, but the main thing is there's not enough beds in the hospitals. Sick, or injured people are literally put on those trolleys they wheel you in on/to an operation on in the hallways. Elderly people have died waiting for assistance. The whole health service is massively underfunded, which has seen a large "brain drain" with nurses and doctors migrating to England, Canada and Australia.
Want to be a nurse? Oh, you're not going to be just a nurse. You're going to be doing the job of 3 nurses because there's not enough, and some other duties too like porting patients around. Want to be a doctor? Enjoy having to get the maximum amount of points in your Leaving Cert possible (final secondary school exams) passing college, then at the end of it all, having to be a junior doctor for a few years, in which your shifts will last 24 HOURS at a time. Seriously. Someone I know who was sick with cancer and had to use a walker was once led down the hall to their bed by a junior doctor, who halfway through had a microsleep and promptly fell against the wall. As they told me, this person looked more on death's door than they were.
OK, now I've given you a perspective on the Irish public health service. Factor in that there's an incredibly low amount of ICU beds, you can see how this is going to be a shitshow.
To answer your second question, in terms of parades, local towns are starting to come out now and cancel their parades, and rightly so. But I guarantee the show will go on in Dublin. Last time it was cancelled was because of Foot and Mouth disease in 2001, which Ireland contained to a great degree, with only a few sheep being having to be culled in one county. Unlike the UK, which lost a shitload of cattle and sheep to it, and cost them billions in the agricultural sector. And that's just it, the farmer's lobby doesn't care enough as they're rural and won't be affected, and this won't affect agricultural exports, so the government, which we don't really have at the moment because the recent election evened the parties out so there's no majority, doesn't care enough about the human cost. The ex-Taoiseach (Prime Minister) who still sort of serves said that there was no worry about public gatherings. So in good news his neoliberalist shitshow of a party is going to be tanked in the next election.
But it's not just Paddy's Day. The Irish Dancing World Championships take place in early April. I would hope that by that stage they'll cancel it because that event attracts thousands of people with Irish descent from around the world to one cramped convention centre in Dublin for 10 days. I hope the exponential growth of the virus at that stage will stop it from happening because it will be a big supplement to the parades fiasco.
In short, Ireland has always had a "sure, it'll be grand" attitude to everything. This time it's going to bite the country in the arse.