Let's see
The zero to 60 should give an easy read .. and these have quite a fine adjustment.
Running 1-30 won't break it if it's over pressured, but having it adjusted over 30 a lot will change it's accuracy.
As you can see the rating doesn't change, it's still max of 350 or something like that no matter what.
1. It is 1/8 and 1/4 all female
2. Relieving means if there is pressure in the line forward of the regulator at say 40 and you dial down to 30 it will release the extra pressure forward of it.
Doesn't really matter which one for your application. Both need adjusted with the trigger down.
3. I'm not sure, I think so but ....?
4.you can get 1/4 and 1/8 npt elbows at any hardware store
I don't like digital myself but again just about anything is gonna work.
I don't like digital because in a garage moisture ingress, condensation, rough handling....all break them.
Ime accuracy is very expensive and the battery is bound to die at the wrong time 2 years from now if by some miracle it's still working at that point.