We updated this walkthrough using version 188.8.131.52 of the Planescape: Torment Enhanced Edition. The EE didn't add any new content, so this walkthrough should still work fine for the original edition of the game.
We used "difficulty 3" (the middle difficulty) for the walkthrough.
Your character is the Nameless One. We often abbreviate this as TNO. Another abbreviation we use is xp for experience points.
A weapon's speed doesn't change how quickly you attack with it. You receive a certain number of attacks per round depending on your weapon proficiencies, and the speed doesn't change that. The speed only affects your initiative -- how quickly you make your attack(s) during the current round.
In general, lying makes you more Chaotic. Telling the truth makes you more Lawful. Accepting a quest without demanding payment makes you more Good. Demanding payment makes you more Evil.
Joining one faction won't prevent you from joining the other factions. At worst, some factions will require you to renounce your other factions first, and you won't be able to rejoin them later. So, for example, if you join the Dustmen and then renounce the Dustmen, then you won't be able to rejoin the Dustmen. So always do your shopping with a faction right away.