If your media doesn’t match your settings in Project Properties, it’s going to re-render. If you want to check what DVDA considers conformed, use File>Optomize DVD.
BTW, I would just go with the regular aspect ratio.
After you do your FX on one event, copy, then Paste Event Attibute (by right clicking). Then, you just have to adjust the position of the FX for each event.
In Camtasia you have the option of capturing just the application window or an area of the screen that you define, so there may not be a need to reset your screen res.
Add all the media files to the project overview. Then set the End Action (what happens after the media play is done) so that the destination of one file is the next one you want to play.