amaniquito

Hi:

FIRST is appropriate. FIRSTLY is common, but grammatically incorrect.

POR TODO ELLO: Therefore
OTROSI PRIMERO DIGO: First additional pleading, we contend...
SUPLICO AL JUZGADO: I respectfully petition the court...
En su virtud: pursuant to/in compliance with/in consideration of [the translation is highly contextual]

Hope this helps,
Amani