Don't know if this has been asked, and I can't find in books. Do weapon qualities/mods stack? For instance I have a curved hilt lightsaber that adds an automatic advantage to the roll. Now lets say I have the same curved hilt but make it superior (which also adds an auto advantage) does that add 2 advantage to the roll?

Yup.

Thanks! That's what I thought just wanted to make sure

Non-quality mods do stack, but you have to be careful with quality mods. Quality mods with a rating (like Defensive 2) will stack if the description says something like "Item Quality (Defensive +1) Mod". However, attachments such as Stun Pulse, for example, says "The weapon gains the Stun 2 quality". In that case, it won't add to an existing Stun quality. I'm not sure if there's a RAW about this, but if it's similar to the way Brawl weapons work, you would take the higher of the mod quality and the existing quality.

In the case of lightsaber crystals, the crystals actually replace existing qualities with the qualities inherent in the crystal, or adds the base quality if it doesn't already exist. So base crystal modifiers normally don't stack.

Qualities without ratings (such as Superior) do not stack. So, you can only have "Superior" on your weapon, not "Superior 2", or whatever. Normally, this is pretty obvious, since most qualities without a rating don't include bonuses (Autofire just does what Autofire does). Superior is an exception, since it adds an advantage and a bonus to damage. Since you can only ever have one Superior quality on a weapon, you'll only ever get the +1 advantage and the +1 damage once. However, other sources for +advantage and +damage will stack with it.

Don't know if this has been asked, and I can't find in books. Do weapon qualities/mods stack? For instance I have a curved hilt lightsaber that adds an automatic advantage to the roll. Now lets say I have the same curved hilt but make it superior (which also adds an auto advantage) does that add 2 advantage to the roll?

Devil is in the details. Always read carefully. Superior adds an Advantage to the check, the curved hilt only adds one if the check is successful.