Welcome to the forum. Theres a forum golf day at Royal Ascot on Friday April 3rd if you are interested. Mike Harris (GM editor) and two of the GM staff - Neil Tappen and Paul O'Hagan) are playing along with 15 or so forum members and it'll all get featured in the GM magazine if you fancy it.
To give you a spin on your questions. I think you have the right Idea. Yes on a par 3 oficially you must hit the green in 1 for a G.I.R and in 2 on a par 4, BUT as you say if your off 18 you get a shot at EVERY hole so if you hit a par 4 on your third you have hit the G.I.R and your there in 2 for your handicap that will leave you two putts for a 5 which will give you a net par.
Its the great thing about handicaps, its designed to keep everyone competitive, no matter how short you might hit the ball!
Great to see more folks joining in. Welcome to the banter!
As far as your questions go, you probably have already seen, I'm in the 'if it's on the putting surface, it's a putt, if not, then no, it's not a putt' camp.
I use Scoresaver for my score recording, and I mark everything in gross. The program then works out what my nets are.
The scorcecard that you can print shows you how many shots per hole you get for your handicap. So it's very easy to be on a par four with 2 shots for your h'cap. Suddenly it becomes a par 6! Easy.
The q? about GIR has been answered, but I say set your sights on what YOU can realistically do. I struggle on long holes but have been known to hit 9 or more GIR!
In the early days (first year-ish, aged 23) I'd be lucky to get on any green more than 100 yards away. The full distance shots rarely went on target, and the rest were dire....I started on about 120 shots per 18!!!