First things first... GO IRISH!
Congrats on attempting your first creation, to quote Obi-Wan Kenobi, "You've just taken your first step into a larger world." :-)
Quotes aside, the program I use is AutoCAD. But I work in the engineering field, so that's what's available to me. It is quite expensive to buy outright, but you can get an AutoCAD LT subscription that is pretty affordable if you want to go that route, and you'll also need a pretty powerful PC. That's really all I can offer as to what programs to use, and please know engineering software isn't optimal for this stuff either, I just kind of make it work. Sorry I can't be of more help, but whatever you do, keep at it! It's really fun and you get to be the boss!