Congrats on the move. Most tikes do NOT have dampers except the Harley Tri-Glide comes with one. Most of the conversions do not. If you are raking it you probably will not need one. Most trikes have a slight wobble around the 20 MPH area as they are slowing down. As long as you know about it you don't even have a issue. It only shows if you take your hands off the bars at that point. Some and only some need the damper for this issue, but they are few. Go ahead and build without it. If after you are done and you feel the need it can be added later.
Just my thoughts. Good luck let us know how it turns out and post pictures.