diegonel

RMRV11:

I think that first or firstly is the same. You can use either of them.

POR TODO ELLO: by all this or therefore: I'd use therefore
En su virtud por In its virtue. It would be good if you gave us some more context
OTROSI PRIMERO DIGO : Furthermore, first I state that....
SUPLICO AL JUZGADO : I plead with the court to....

hope it helps