You can use both and make a real blocking machine?
You should yep 
you can add Centurion’s party formation too! (by having a centurion in your party)
But don’t forget your block rate is always influenced by the block negative stat of ennemies ^^
And since it’s not flat % for finestra (example you have 100block rate, and use finestra you now have 130 block rate minus ennemi’s block bypass) you will block better but it doesnt’ change the fact you can’t be a great block machine as you can be in other MMORPGs (like archeage where you can get 80+% block rate)
Wait how can you use both Finestra and High Guard? Aren’t they both stances instead of buffs (although they show up as buffs)? Like they literally change how your character stands and holds their weapons. Are you sure they allow you to use both?
Oh they are stances, well i’m not sure then. Cause for example Gung ho and guardian says they can’t be used at the same time. But for finestra and high guard it’s not said :x
Well I said stances but I’m not sure if that’s the right word since Kneeling Shot is an actual stance without SP use or CD however Finestra and High Guard actually do change how you hold your main and side weapon/shield but with a CD and SP use. If you can use both, then great but what would the animation show since both have different forms?
Thats is my doubt, but I don’t think theres a lot of Petalsta C2 Hoplite CX in this beta to answer me.
Well if it’s an animation change it chould just use that last form anyway like in lot of “certain games” (lol) where buffs changed your class color and only the last one remained visible. ^^