Hi Kaleb and welcome to SD.
Not quite sure what you're asking with your first question, but young adults will start pairing perhaps at about 1 year old, usually 4-5 inches or more by then. It may take two discus some time to actually develop the pair bond and spawn. If you provide good water conditions, they usually do. This also assumes you have a true pair, which is generally hard to know until after they've spawned and the fry have hatched.
A pair my spawn in a community tank if they are comfortable, fighting off others to protect a corner or something. This is not usually a successful environment for raising the fry. You'd want to get the pair their own tank and let them start over.
Just a quick response but feel free to ask more questions!