ὠφελήσασι is the dative of the aorist participle for ὠφελέω, but notice the syntax in σύνισμεν ἡμῖν ὠφελήσασι, where σύνισμεν (which takes its object in dative) has two objects ("we are aware of ourselves", "we are aware that we helped"), where the second object, the participle, comes as an epithet to ἡμῖν. You will encounter such a syntax pretty often.

In the phrase "τὸ τῶν λόγων", the article "τὸ" refers to a missing/implied word, e.g. "the gift of words". In translating I kept this implied reference by using the word "something", which is equally vague.

Your translations will be fine when, of course, are right, but also when they are natural, not like automatic/machine translations. You need, let me say it again, to work much slower, think much on a sentence, to find the right meaning and then express it in a natural way for the language you are translating to.

Ok, thank you for the advice. I will try harder, I'm already having difficulty in finishing the translation for this letter, but I will think more on the sentences.

Thank you again!