Guide:Sharpshooter
This is a guide for a build that focuses on dealing 
Physical damage from a distance.
Overview
Core components for this build include:
- Any kind of Hand Crossbows in each hand
- Sharpshooter feat
Sharpshooter provides additional damage for a penalty to accuracy. Attacking from the distance helps to mitigate the accuracy penalty (high ground, hiding) while Hand Crossbows allow to use bonus action to make attacks. Which the bonus damage from Sharpshooter this additional attack more than compensates the fact that Hand Crossbows have less basic damage compared to the Heavy Crossbows.
Having minimalistic core this build allows many approaches from the class perspective. The most notable options are:
Battle Master fighter
Hunter ranger
Gloom Stalker ranger + 
Assassin rogue
Attack count
This build benefits greatly from both: doing multiple attacks for each action, having multiple actions per round.
That's why 
s, 
s and 
s are good class choices - all of them get an 
Extra Attack and can attack twice for the cost of one 
Action.
There are several ways to get multiple Actions for each turn of the battle with the most notable:
Hastened
Elixir of Bloodlust
Action Surge ( only)
This results in having, on average, 2-3 Actions per turn plus one 
Bonus action.
Ability Scores
Range weapons use 
Dexterity as the primary Ability Score so it should be maxed.
Secondary abilities are up to you. Constitution never hurts. For spell casting s might want to improve Wisdom while s - Charisma.
Races
This build does not rely on any particular Race.
Halfling is a good choice because of the Lucky. Their low movement speed is less relevant - as a range striker you don't need to move much around battlefield.
Drow with Superior Darkvision is nice in the darker settings.
Dragonborn gets resistance to a damage type - especially useful for 
Fire damage, which is quite frequent in BG3.
Battle Master version
This version of the build performs great early and mid-game, while fully outperforming other options in the late game.
Action Surge and
Other class options
Beast Master: overall a viable alternative for the approach.
This subclass does not bring improvements to the range combat hence putting the option into "Other" section. Still beasts are strong and overall Beast Master version will bring both firepower as well as survivability and flexibility to the party.
Champion: an alternative option for the approach.
Main benefit of this version is an improved critical (equivalent to about 5% overall damage increase). For a ranged build a Champion is more interesting than for a melee one - there are a lot of ways to guarantee crits for melee strikers in bg3. Still Battle Master Manoeuvers provide a comparable damage increase together with a ton of utility and flexibility.
Do note that Champion subclass makes more sense for this build if you try to minimise amount of long & short rests.
College of Valor: an option for a approach.
Brings a full caster in addition to getting 2 attacks (as a ranger or a fighter). 
Bardic Inspiration brings damage increase comparable to a Battle Master or a Hunter.
The main upside of the approach - ability to utilise Concentration way better. Main downside - bardic inspiration takes a Bonus action to be used, which will make this version of a build doing less damage comparing to some fighter and ranger options.
While having an access to the awesome Bard's spell list is great, with this build you are still usually going to use your Action for attacking with the ranged weapon.
Thief rogue should also be a viable choice (that I have not tested yet)