Due to the fact that I travel a lot and cannot shoot often I will be an oddball. Also, I usually bring 2 or 3 guns per session, normally all in the same caliber.
Q1) Enough mags to load 50 rnds per gun. Usually that means 7 or 8 mags. Some guns I have enough for 100 rnds (Glock 20).
Q2) At least 1000 rnds. Due to the time commitment, diffuculty and other problems, it is not worth it to bring less. Although I commonly only shoot about 700 to 900 rnds.
Q3) 3 to 4 hours is normal.
Key point to add though. I try to work on one topic only when I am at the range each session. For example, this week I was testing out a 10mm and I was just concentrating on control of the recoil. I was watching the sights, but not really sighting. I was focusing on watching exactly how the gun recoiled and operated. I was keyed to working on the flinch problem.
Some days I will just focus on trigger control, other days I just focus on front sight only, some days it is just DA or reloads.
Now when I am in country for a while, then I work on all of the parts at once, with less rounds and multiple times per month.