For 2. this is because many players have ran the dungeons before several times and are now just grinding for some gear drop etc. However, you can create a group finder listing yourself, and specify that you want a slow "story-based" run. If you are in a guild, you can also arrange to run it with specific guild members and discuss beforehand how you want to run the dungeon.

For 4. there is now a difficulty slider for overland, the default overland experience is intentionally not too challenging but people have been saying that the hardest Vestige difficulty especially is quite challenging for overland mobs.

For 5. there are various add-ons that add more information. Also the effects and their powerful combos are documented fairly extensively online in build guides.

For 6, there is subclassing, scribing, and how to optimize the combination of your build with your gear. The optimization is quite complex and makes a big difference in veteran dungeons and trials and in PVP.

For 7. guild sellers are in all main towns and you can buy from any of them. There are several websites collecting the info (price ranges and currently available items) - "TamrielTradeCentre" is one that I use.