Not familiar with the Rossignol, but I have the Dynastar Big Trouble (a wider version of a similar construction as the Nothing But Trouble). I find my BTs great in a variety of conditions; with a narrower waist, the Dynastars that you are considering are worth a look. You may find similar skis at either www.backcountry.com
. Both are reputable sites that do a lot of online sales. There are also some great shops represented on this site (SierraJim and Dawgcatching each have shops with great reps). Be sure to do your research. However, the Nothing But Troubles may be a great starting point. Remember that a twin tip will ski short because of the raised tail.
As for bindings, your height and weight will be helpful, but my guess is that any 12-din binding will be sufficient. You can get Rossignol Axial2 120 bindings or Look PX12 bindings quite cheaply and they hold up well.
To answer your question about turning radius and slanting sidewalls, others will offer more correct advice, but here goes: turning radius has to do with the sidecut of the ski. A higher turning radius will mean a straighter sidecut (less hooky in crud but not as easy to turn on groomed). More sidecut = more turnability for short turns. For what you are describing as wanting to ski, the Nothing But Trouble (or similar ski) should be fine. As for slanting sidewalls, that refers to the sides of the ski slanting out wider at the base than at the top sheet. My Volkl Karmas have this sidewall construction and they tend to have a bit more edge hold on firmer conditions than my BTs, which have vertical sidewalls. Not a big deal either way on most days to me.
As for boots, my strongest suggestion is that you research bootfitters in your area (have you checked the Ask the Boot Guys forum on this site?). It is not worth buying online only to find that you are in the wrong boot. Be sure to get a shell fit that is 1 to 1.5 cm behind your heel and be sure to try on a variety of boots for a fairly lengthy time before your buy em. Not a process to be rushed for sure.
Hope this helps a bit.