Haz - you asked about playing Sonic Synth 1 sounds? If you have projects that use SS1 sounds, then it's probably a good idea to keep that (SS1) installed. For a little while at least.
SS2 actually has a bit of a "best of" SS1, but of course it's massively upgraded. You'll probably find that once you start getting in to SS2, you won't bother with SS1 anymore.
As for SONAR, I don't use it, but I've heard/read that people have had much better experiences using the VST plugin version with SONAR's wrapper. You should try both though, to see which works best for you.
Hope that helps.
Forever,
Kim.

