^It really depends on a lot of different factors, and there's no way of predicting what exactly someone's symptoms will be....
Tapering slowly down to a very low dose of buprenorphine will definitely make the symptoms much more mild and bearable, but as to whether or not you'll have insomnia and RLS, nobody can really say...
3 weeks is plenty of time to become dependent, and even very small amounts of suboxone will stave of almost all withdrawal symptoms.
The only situation I can think of where someone would do a 3 week long suboxone taper without a habit, would be if they were in a rehab facility and had lied about their opiate use so that they would be given suboxone. I've actually seen this before...people in rehab getting absolutely bombed from the suboxone they were being given to taper from their nonexistent opiate habit! Absent a situation like that, I see no other scenario of someone performing a suboxone taper with no habit!