It's wonderful to hear you're planning a visit to Northern Ireland!
There are many lovely gems for you to discover all around and I highly recommend to all the travel tips for places to visit here
Regarding your inquiry, it's absolutely safe for your to visit any area!
Additionally, you won't need an International Driving License in any case. You can verify this directly on the following guidance about Driving in the EU after Brexit.
I'd also suggest for you to contact your car insurance company for more info!
Hopefully, this information sheds some light on this particular area for you.