Looks like most of your questions got answered. I would just say this,
1. Don't get in the habit on picking up too much loot. 99.9% of it is useless, especially in the acts. If you're filling up your inventory in a zone and having to go back to stash, you're picking up junk to sell to vendors.
2. Use an item filter
3. Don't use too many skills at once. It's better to just one or two damaging skills and as many support gems as you can linked to them. Each support gem that you link multiplies your damage. Rest of your gems should be ultility, like a totem or something to help against bosses, an aura or two, a curse, a movement skill.
4. Use a couple websites for the smoothest experience, although it's not required.
- https://www.pathofexile.com/trade this is the official trade site. you can look up items and copy a message and send it in game to people to buy. can also search your items to see what people are selling them for to get a rough idea if they're worth anything. you'll quickly see that 99.9% of the loot you have is worthless
- https://www.filterblade.xyz/ grab a loot filter from this site, there's good descriptions. For starting, I would recommend a normal strictness.
- https://www.poelab.com/ when you get far enough in the game to ascend. this will help you.
If you need help in-game, my id is GamerJatt