Styrene is going to accumulate based on what you are building. It's easiest to advise based on a project. BUT, this is internet modeling and we all have answers.
Sheet, 0.020 and 0.040 to start. Strip: 1x4, 2x4, 4x4, 1x6, 2x6, 4x6 and 6x6 will do common trim jobs. For bracing I use...