When I want control over a number of simultaneous tracks i.e Guitars, is it better to Group them, or send them to a Buss (created in Vst connections)
is there any real difference between the two?
D 
What do you mean by “group them”. you can group audio events, but not tracks.
It’s the same thing - another word for a group in Cubase is a buss.
Use a group track, or even folder track. That will give you a fader, inserts, sends, and all the other submix goodies you want.
VST connections is really for managing inputs and outputs, such as microphones and monitors. Not what you’re looking for, unless you want to send all guitars to an external mixer.
Not true - you can just as well create your group and FX channels there.
Sure… but it’s pretty pointless doing it there. Generally it’s for managing i/o .