Also I just want to clarify, there are "two" different Avernum 2 and 3's. Am I to assume those are remakes of the originals?

There's probably a second Avernum 1 as well. I believe the first remakes (Avernum 1-3) didn't have subtitles. The second remakes have the old subtitles from when the games were called Exile.

The re-remakes are:

Avernum: Escape from the Pit
Avernum 2: Crystal Souls
Avernum 3: Ruined World (the one released today)

Avernum 4-6 aren't getting remade (yet).

There's a lot of useful help at the official Spiderweb Software forums: http://spiderwebforums.ipbhost.com/

A couple things that aren't obvious but aren't spoilery:

1. Some skills are cumulative through your entire party. That is, when a relevant skill check happens, the game uses the total of all characters in your party to see if you have enough. If all 4 characters have 2 in one of those skills, your party has an effective skill of 8. Tool Use, Arcane Lore, Nature Lore, and First Aid all are like this. The first three have soft caps, where totals above a certain level are wasted, because there aren't skill checks higher than a certain number. The Spiderweb forums have all kinds of spoilers if you want to know what the numbers are (and the hint book will have it too, obviously). The re-remakes and Avernum 4-6 do things a bit differently, since Vogel changed how things work in the remade games, but largely the same idea.

2. Beyond the cumulative skills, unless you are playing on Torment difficulty, don't worry overmuch about twinking your build. You can win with the starting party, even though it isn't optimized perfectly. People go through singleton on Torment.

3. Even though it's doable, just be prepared to get smacked around a lot. Save often. Avernum is of the same philosophy as Witcher 3 in that it sprinkles much higher level encounters in and around lower level areas. You're intended to come back later. If something wrecks your face, go do some other stuff and come back and get revenge.

One other thing of note:

For the Avernum remakes, you want characters to focus on one thing only; the only real exception would be giving spellcasters some weapon skills so that they can use battle disciplines (the one that gives you more AP this turn is particularly nice).

For the original Avernum trilogy, this does not apply; hybrid characters are worthwhile, and there are no battle disciplines in those games. (5 and 6 introduced them, I believe.)

I second what dtgreene said. Have dedicated party members. I usually do a sword & board fighter who switches to dual wielding later in the game after getting some powerful magic swords. I usually have another fighter who I split between melee and ranged weapons. Sometimes this is a polearm wielder, other times it is another sword and board fighter. Then I have a mage and a priest. One of the characters will pickup Tool Use every so often, and one of the characters will pick up Cave Lore every so often so that I can keep a few points of each in the party.

I don't know if I see a point in the higher difficulty settings. The only thing it seems to change is increasing enemies' resistance to everything by an inordinate amount. It's a great game though with a fantastic story.