I always wondered if my knees would hit if I had the chopper bars. Your balance on a recumbent is achieved by keeping your back centered on the seat back and relaxed. Set up your seat for seat to pedal distance, and then set your handlebars. There is tiller with the Stratus, so it's best to get used to it with your seat properly set. I didn't get the chopper bars on my 2007 Stratus LE, I got the other option, the B32 riser with the B37 bars. It's a very comfortable setup for me. Carl will know which parts you need for that setup.
Yes, many folks have a problem balancing at slow speeds. Sometimes if I haven't ridden for a while, getting down to 6 mph I start to wander left and right a bit. The key is relaxing as much as you can. There is also a bit of "pedal steer" with your feet out in front of you. As you push down on a pedal, it can tend to push the front of the bike right or left. It's another thing to get used to.