Are you thinking of keeping a persistent team? Also note that you can also get hirelings once you find Withers and get him in your camp.
open the locked chests/doors
You're going to want someone who is proficient in Sleight of Hand to disarm traps and pick locks. Astarion's pretty good at doing that. You should also keep an eye out for a piece of equipment called the
Gloves of Thievery (provides advantage on Sleight of Hand checks), which you can get in Act I.
You're going to need a decent Perception score, and getting the feat Dungeon Delver will let you make Perception checks to detect hidden objects with advantage; it also has the added bonus of also providing advantage on saving throws against traps, as well as providing resistance against them.
Which spells should the player character have relative to the companions with the focus on spells that expand the story/quest options as well as access to as many locations as possible such as Speak with Animals, Speak with Dead, Detect Thoughts, Mage Hand, Feather Fall, Knock, Misty Step, & Fly.
Keep in mind that some of the spells mentioned above also come as scrolls or potions (the latter of which can be crafted), so you probably won't want to prepare or acquire the really situational ones like
Feather Fall. A few companions (like Karlach and Wyll) can gain access to
Speak with Animals through class options. Early on in Act I you can get
The Amulet of Lost Voices, which allows the wearer to cast
Speak with Dead.
Misty Step is always a great combat maneuver.

As someone who fell into the trap of thinking 5e rules would be mostly preserved, reconsider taking
Mage Hand; it only lasts for a minute and you can only cast it once per short rest.
It's fine if you want to limit yourself to certain races or classes; just note that there are unique dialogue options that may pop up if you're playing a bard or a tiefling, for example.