RE FX vs. Groups;
This has been a common source of confusion ever since Cubase SX was introduced 20 years ago. I’ve posted many times about this.
The short answer; the only difference is the default color.
I’ve always maintained that we should have effect “returns” like a traditional mixing desk. The main difference being that an effect would be hard-wired to the top of the return, not inserted into a buss.
And, of course we’d need an effects “rack” to neatly host all of our effects plug-ins where you could quickly go and make adjustments with intuitive ease. We actually had an effects rack in Cubase VST days.
Until Cubase SX I had never heard the term “effects track”. And at the time I think you had to first create an effects “track” and then go back and insert an effect yourself. It’s since been refined so the effect is chosen, inserted and labeled when you create the track. I’ve long since submitted to the design.
Please excuse the rant. I continue to carry this flag and wave it whenever I get the chance.
As raino points out, Summing Mode should solve the other part of your question.