Baldur's Gate uses a classic D&D system of attributes that determine how well each character does particular things: Strength, Constitution, Dexterity, Wisdom, Intelligence, and Charisma.
Pacifist run players are faced with far more challenges and constraints overall, but when it comes to attribute scores at character generation, they actually have a definite advantage, since combat-related attributes can be significantly downgraded during character generation.
Generating Attribute Scores
To get your initial scores, you roll virtual dice to get various starting numbers for each attribute, then allocate these to the various attributes your player character has throughout the game. (Note: In D&D tradition, BGEE is a game where you have relatively few chances to increase your initial starting attributes, which typically don't change at all during level-ups in which only new skills are increased.)
Impacts combat damage, but also isn't useless on a pacifist run since it determines how many pounds of treasure or items each character can carry around. However, before investing points in strength, it's worth nothing that you can easily recruit lots of strong warriors as NPC allies throughout Baldur's Gate. (All you need to do to stop them from automatically trying to slay all who oppose you is to click off the automatic AI button.) These strong NPCs can then help even the weakest mage or thief carry hundreds of pounds of treasure out of various lairs of iniquity— as long as you've also got a mage with you to cast invisibility on them to keep them from getting slain by multitudes of foes while they're busy carrying around your treasure. (An invisibility potion could also be used, but these are rather scarce in the first half of BG1.)
This determines how much endurance, hit points, and stamina a character has, and having too low a score can cause the character to be damaged easily, or get fatigued more quickly after hours of travel. We never noticed any particular problems using scores as low as 9-10 for our Enchanter of Thief characters though, other than the predictable "modest" number of hit points.
This skill is important to the Thief, since it supports their skills and the probabilities of success with actions like picking locks, hiding in shadows, pickpocketing, etc. I believe there is also value in it for non-thief characters when it comes to their chances of dodging attacks successfully.
This is one of the more counter-intuitive attributes: For a cleric, Wisdom is the most important attribute, determining how many spells they can cast, and how well they cast them. However, it rarely seems to be important as it sounds for other types of characters (as far as we know), other than that you may need a minimum score of no lower than 9 to be able to use wands, which are definitely very useful assets in a pacifist run.
Intelligence is the prime attribute for all the "Mage" classes (i.e. normal Mages, and specialist mages like Enchanters, Illusionists, Conjurers, etc). It determines their ability to learn new spells (which they scribe into their spellbooks and then memorize during rest), and how effective the spells they cast are when used. (Apparently "Wisdom" is not as important to a mage as one might guess, and the same is true for Clerics and "Intelligence".)
This attribute comes into play in several ways:
In the first place, there are a number of unpredictable situations scripted into the game in which an in-game character will change their reaction to your lead character based on his or her Charisma score. Sometimes this results in a nice but non-essential bonus, like being given a larger reward than anticipated, or other situations where it determines the difference between an NPC becoming hostile or not. (We've also seen remarks indicating that it might impact the effectiveness of Enchanter spells, but we're not sure if that's true or not since the actual formulas the game uses are hidden.)
At shops, a high Charisma gives you a bonus by having merchants reduce costs to somewhere around a maximum discount of -20%, which adds to a lot of gold saved in the long-run. (And it's usually worth saving as much gold as you can: There are a number of particularly excellent magical items in BG1 that are only available in shops for high prices, and which can make a pacifist run a lot easier and more fun.)
One note: Those unafraid to use game guides and maps to locate pacifist run treasure can pretty easily come into possession of a magic book that increases CHA by 1 point permanently, and thieves can also optionally nab a cloak fairly early in the game that increases CHA by 2 points as long as the cloak is being worn.
NOTE ON ALLOCATION FOR PACIFIST RUN:
After doing the research needed to figure out what to do at character generation, a pacifist run player can take advantage of their non-combative nature:
Our Elf Enchanter in group 1 started with 18 INT, 18 CHA, 14 DEX, and a meager score of only 9 in each of STR, CON, and even Wisdom, but was still able to use wands with no obvious penalty, as well as easily scribing any mage spell.
Our Halfling Thief from group 2, in contrast, started with 19 DEX (since a +1 bonus is given to Halfings, as well as Elves), 18 CHA, and 15 Strength (since we'd already maxed our more important DEX and CHA scores), leaving CON, INT, and WIS at 10 each.
What both of them had in common was that they needed to temporarily bring physically stronger NPC allies along with them at certain times— not to fight, but rather to carry away all the treasure and heavy quest objects that these two leading men were both too physically weak to pick up and carry away by themselves...