1. It's a 50% chance to avoid any effects (including damage) from a trap that would otherwise have affected you.
2. There's a silent running perk, but you get it as a reward from a quest. You get the quest form one of the NPCs in your faction.
3. The ghoul is on your side, he will help you fight the geckos. And I believe all the critters in the tutorial are weaker than normal mobs you find later in the wasteland. So no, it's not meant to be particularly difficult.
4. The tutorial is there to help you learn the basics of the game, and to be a fun introduction. If you do all the stuff in there you get enough experience points to level up a few times, which is always nice.
5. There are currently 3 type A drugs which last for one hour:
-Blood Moon: +2P, +20CC, -20CR, -20 Bleed Res.
-Mentats: +3P, +1I, -8DT, -5DR, -1S
-Buffout: +3S, +2E, -1A, -3L
Then there are 3 type B drugs which last for only 2 minutes:
-Psycho: +2S, +10DT, -20% AP regen, -5P
-Afterburner: +5 AP/s, -30DR
-Voodoo: +20% run speed, +15DR, -10 to all critical rolls, -3L. After 2 minutes you get winded (unable to run) for 30 seconds.
6. The requirements to enter the dungeon are mentioned in dialogue when you try to enter. Currently, the Phoenix Archives dungeon requires 4-6 players with at least tier 2 gear. The Hell Hole dungeon requires 5-7 players with at least tier 2 gear.
7. No idea
8. The minimap doesn't show you where you are. But if you right click on a map, you can add a marker. You can use the marker for whatever you want, for example to help remember where you hid some loot or something. You can only have one marker at a time though, and unfortunately it's a bit buggy if you switch chars or so. But it's better than nothing I suppose. It's not a glitch anyway.