I powered through another run on vanilla, no mods, and here are my "quick" thoughts:
1) Character Creation:
Pick different classes and races to create some visual separation (unless going with a clone war theme).
Pick diametrically opposed alignments for the most fun factor (very self serving/greedy, very heroic/altruistic, super violent/oppressive, etc.). From what I can see you are never penalized for having lawful evil, chaotic good, true neutral, etc. in the same party. In fact, it goes a long way create distinct personalities, as well as some funny comments in the cut scenes.
Don't be afraid to Roll your stats... spend 5 mins, focus on stat 5 of 6, and don't stop until that spot is 13+... you now "most likely" have great stats.
There are widely available Strength and Constitution items... so you can be soft(er) in those stats (almost better that way).
Pick wisely on faces, hair color, etc., no way presently to go back :)
You can win the game infinite ways. All classes are effective, but some, a bit more than others. Do not worry about if you are making a good or bad decision, you will have fun if you like the way your character plays. Which means, if you expect massive melee damage out of a wizard, you will be disappointed (can tank with certain spells, just not a melee damage king). So no regrets.
Also, if totally new, I suggest: Paladin (any), Wizard (any), Cleric (any), and Rogue (Shadowcaster) or Ranger (any, but Low Life Background). This will help you experience a lot more of the game and make most of the game easier on you. To be fair, you can power through the game with all Fighters if you want, like I said, no regrets.
Surprise is incredibly powerful in this game. It is like getting 1.5 rounds of uninterrupted damage, debuffing, debilitation, etc. So use cautious, don't move really far in front of you on the map (can't stop easily if you see enemies). Use it to win, or ignore for a bigger challenge.
On "random road" encounter, use your spells, smites, special skills, without restriction. No need to conserve, you will sleep between the next fight or map.
When tackling actual campaign areas, (e.g., Lava Forest, Copperan, etc.) balance resources. Decent rule is to have everyone use "one" expendable skill each battle, going higher if a boss (or party in trouble).
So many ways to defeat an enemy, so no need to overthink it. However, if looking for advice: use surprise (attack first), keep party together (no solo rushing), use AOE crowd control or damage (softens up enemy), don't use spells to heal (quick rest is powerful), remember as game matures, more resistances (keep bludgeoning weapons around, don't only spec fire spells, etc.), armor is your friend (harder to hit the better... can make a case for Iron Legion feat for casters), everyone needs a reliable ranged attack (bow, cantrips), and not all offensive cantrips equal (firebolt, with ice bolt, necro recommended - best to have to-hit chance, not roll to save).
Light cantrip... if you have access, take it. Invaluable. Also, Sparkle is a hidden gem.
General rule: Easier the difficulty, the more important offense become. On Cataclysm, the inverse is true... damage mitigation is everything. Half my spell book changes and many combat style decisions.
Magic weapons matter to hit some creatures... so sometimes better to swing +1 mace (1d6), instead of regular longsword (1d8).
Money arbitrage is more complex than it seems (for me). You would think if you are selling items to factions that are both "Living Legends" (status) the coin offered to buy your treasure should be the same... incorrect. Sell to Gorim, start to finish.
Need plans to make magic weapons, a new vendor appears at the ruins (library) site, who can sell you anything for a reasonable price.
Some treasure drops are random, but don't worry, the big stuff is fixed.
Don't bother making or buying anything until after level 6... most stuff drops or is available. Save treasure for stuff that is hard to find or impossible (+2 plate, +2 shield, fire giant belt, +1 ring of prot, +1 cloak of prot).
Useful weapons/items to make: Ice Long Sword, Fire Long Sword, Lightning Long Sword, Punisher Axe, Lightbringer 2-hander (all add extra damage, and +1 to hit) - irreplaceable for melee members, like fighters/paladins/rangers. Black Viper (rapier) for dextrous character.
When residence opens for you (not staying in tavern anymore), there is a chest of useful stuff.
5) Have fun
The game is on rails at points, but that is the fun, the DM (dev) is telling you a story. When playing a tabletop adventure, could I choose not to descend into the underworld? Sur, but eventually a good DM will push you there to move the story forward.
Enjoy the tactical environment and decisions (verticality, objects, cover points, etc.)
Take in the scenery, some really cool spots you travel across or fight around.
Do the side quests, most are fun, with decent xp/items. One side quest has a great item and irreplaceable component.
No regrets, just play the adventure. If you make a bad tactical choice or a string of bad rolls (I once rolled in one turn: 2, 2, 3, 1, 1,), play it out, you can/will recover. If things go south, you can always reload :)