Hi, and welcome to the forums! (I'm very new as well). The pointers I'm going to present here aren't necessarily build-oriented but they have really helped a friend (a D&D ttrpg veteran) to have a very solid start with the game in levels 1-4 on Tactician difficulty.

The two bosses you listed are among the most challenging combat scenarios if you are lower than level 5, and it's really early to talk about builds or multiclassing having a huge impact so early in your playthrough. I think in levels 1-4 (if you're playing on the hardest difficulty) it's better to have very solid AC levels and save rolls on the squads you use for the toughest batttles and sidequests. I recommended my friend certain gear and weaponry you can acquire from vendors in the Grove and Goblin Camp. The pieces of gear can be distributed among your different companions and your Tav, depending on classes and preferred squad composition.


Starting gear
Lae'zel starting medium armor is pretty solid in the early game (AC 15). All her gear providing +1 to skill checks (CON saving throws, +1 athletics, IIRC) is good in the beginning levels.
In general, pieces of gear (helmets, bracers, rings, amulets, boots, etc) giving a bonus to AC and boosts to some kind of saving throws are all usable and decent at the very start. I started to gather rare gear (blue color-coded stuff) mostly at levels 4-5.

DRUID GROVE

Dammon and Arron (some gear pieces are offered by both vendors)
- Safeguard shield (+1 to all saving throws). If you don't use a shield with your Tav, it's excellent for Shadowheart.
- Gloves of Missile Ensnaring (sold by Arron)
- Hunting Shortbow (sold by Dammon)
- I'd suggest at least one +1 light crossbow and one +1 heavy crossbow, but some players might be ok with just one of them.
- A few select uncommon weapons +1 based on the characters you use. Be choosy because they are expensive, prioritize your Tav proficiencies and then the companions that you use the most.

Auntie Ethel
- Corellon's Grace (staff for spell casters)


GOBLIN CAMP

Grat (goblin trader)
- Gloves of Archery
- Returning pike


Special note for armors
The 3 armors I feel like I got the most bang for my buck in levels 1-6 were:

- Chain shirt +2 (Medium armor, AC 15) - sold by many vendors after you hit level 3.
- Chain Mail +1 (Heavy armor, AC 17) -sold my many vendors after you hit level 4.
- Padded armor +2 (Light Armor AC 13) - I used it on Wyll and Astarion for quite a while.

Caveat: Depending on which sidequests you tackle first, some of these suggestions may not be as important when you're at level 4. The vendors I listed have other useful items, I'm trying to provide a minimalist table to strengthen your squad in the early game.