If you currently have Platinum installed, you don't need to install the content again. Just choose the option to install only the core program.
It picks up most things automatically (e.g. themes, templates, colors). I had to add some VST scan paths and correct a couple pathnames on the Folder Locations page. After installation, though, any configuration changes you make to the old program will not affect the new one, nor vice versa. The new installation simply copies your existing INI files into their own folder, the same way SONAR did when going from one major version to another. It appears to use the same registry keys for inventorying plugins (for now), although it will insist on running a fresh scan the first time you start it up.
New Cakewalk resides in "C:\Program Files\Cakewalk\Cakewalk Core\Cakewalk.exe" and doesn't conflict with your existing SONAR installation. You can even open both SONAR and Cakewalk at the same time to compare them and verify everything's where you want it (I took screenshots of the SONAR Preferences pages, which was easier to read side-by-side on one monitor).
At this time, you can simply think of New Cakewalk as the latest update to SONAR. It'll open all your existing projects, find all your VIs and effects, and save them to the same place in the same format as before. Until they make some fundamental change to the project file format, you can switch back and forth between SPLAT and Cakewalk.exe without complications.