One - if I want to create, for example, a "lightning" material for a lightning-breath attack, should I add a paralysis syndrome in the material definition itself, or create a separate tissue and define it there?
Two - what should I set the temperatures for 1.the lightning material so it causes immediate burns while remaining a "gas", so that it doesn't linger around 2.a frost-breath material so that it causes frostbite?
Three - going from the previous two - would it also be possible to create an "acid" material that causes burns but unlike the lightning is a liquid and lingers? If so, what values should I change so that it remains in that state at said temperature, instead of becoming a gas?
1) you generally define sydromes on materials. for the examples you provided you need to have a syndrome that works on contact, see the syndromes page in the wiki
2 and 3) you need to set the materials' melting/boiling points such that they are in that state at normal temperature levels. you can use extreme values here because the materials arent used in any other way. so use a boiling point of like 9000 for things are meant to be gases, and a low melting point + high boiling point for things that are meant to be liquids.
unsure about gases, they do tend to linger for a while afaik. dont know at which point gases become so hot that they burn stuff but if you want to be sure use something like 15000 fixed temp. no syndrome needed.
regarding frost bite, not sure if thats possible, but you could conceivably make a syndrome that has frost-like effects (slowing down, blisters, etc) or some kind of material interaction snydrome.
acid is fairly simple, just have a liquid mat with a contact syndrome.