Hi John I am not Paul and as a User nor someone in any way related other to VSL than you.
Have xou seen all Westlake Pro Videos about Synchron-Strings and Player. Presmably most of your question might be answered here.
1) As far as I understand you should make a difference between "real" recorded Legato and only scripted Legato many Kontakt Libraries offer. (Meanwhile of course also the meticoulosly sampled VSL-Legato is obviously organise with scripts but more to bring to gether the most fitting samples than chnaging the pitch of any or cheep "scripted legato" things like that)
2) Yes "massive of samples" but 1) with SSD's a powerful System and a Preload at 3172 it will be realistic to work with as we are used to.
3) As far as I understand I can not see the velocity VSL tends in any way "to get rid of"Velocity XFade. I fear you might perhaps misunderstood something.
4) the most detailed information I know you can get in the linked 2018 VSL Westgate Pro Sessions. As far as I understood, the more or less 'two dimenional' Matrix-system is replaced with a still more powerful but at the same time musically better focused (8) multidimensional (System) based on aticulation/sound dimensions which each can provide a bunch of variations either to scroll or to switch and if I understood right you still can chose yourself wether you intend to switch with Keyswitches or CC, while CC's are of course "betterr" if you want to use any kind of XFade in a certain "dimension".
As far as I can see the Synchronplayer is meant foremost for Synchron-Libraries to make their power in the most convimient way available. Previous Libraries are at least intended to adapt to the Synchron Player (which imho would especially make a lot sense for all dimension libraries) but of course we presumably have to wait that they start doing this until at least everything with the exiting Synchronlibraries works fine with the Player. So we just need some patience.
... may it be may or may it not be may 😛