The subway system (affectionately known as 'The T') is the best way to get around. It's safe, inexpensive and is faster than driving during about half the time. You can get a contactless tap & pay CharlieCard 7-Day Pass for $22.50 at one of the automated kiosks.

From the Airport, get on the Blue Line towards Bowdoin. Trains come every 5-10 minutes. Get off at Aquarium Station (about 6 minute ride), and the North End will be a 10 minute walk from here.

Boston is rather small, you'll probably find yourself walking most places downtown.

The T doesn't super late, if it's after 12:15AM - I'd recommend an Uber instead. Boston is also not a very 'late' town, with most bars closing between 11:00 and 2:00AM, with a 1:30AM last call. If you really need to drink later, Encore Casino in nearby Everett is 24/7 and serves booze until 4AM.

For Irish Pubs, my favorite is The Druid in Inman Square. It's a 10 minute walk from either Green Line E-Branch Union Square Stop or Red Line Central Square Stop. Outstanding food too.

If you want something more casual, Emmett's is downtown and always a good time. They do live Irish music from time to time. Other great Irish pubs include The Burren, JJ Foley's, Brendan Behan Pub. The Black Rose is fine too. If you're up for something a little different, The Haven is a Scottish Pub that is adored.