Ὦ ξεῖνε Μάρκε, χαῖρε. Ἀεί σου ἀναμιμνῄσκομεν [ἡμεῖς, ἐκείνοι ὅτι ἐν Ἀργυρᾷ Ἀλὶ σᾶς διδασκαλίας ακολουθοῦμεν].
Oh, friend-guest Mark, be happy. [We, those who in Silver Sea yours teachings follow], always remember you.
Some observations on your original text “Ὦ ξεῖνε Μάρκε, χαῖρε. Ἀεί σε ἀναμιμνῄσκομεν ἐκείνοι ὅτι ἐν Ἀργυρᾷ Ἀλὶ σᾶς διδασκαλίας ακολουθοῦμεν.”:
1. Ὦ ξεῖνε: The offered ancient Greek text is as close as possible to the Attic dialect, as your original one contains forms of other ancient dialects, e.g. ξεῖνε is from the ionic dialect, σᾶς from the doric one, Ἀλὶ from the Homeric language.
2. Ὦ ξεῖνε Μάρκε: Ancient Greeks, when addressing someone, used the vocative case “
ὦ ξένε” either for a stranger or for a foreigner, but also as a politeness form for somebody whose name was unknown and the address “
ὦ ξένε” came to mean something more than “
ὦ φίλε”; so, “
ὦ ξένε” and a proper name can’t go together; you will have to choose between just “
ὦ ξένε” and “
ὦ (proper name)”, adding if you like “φίλτατε”, the superlative of the adjective φίλος, in front of the name. Be careful with the vocative case of the proper name.
3. Ἀεί: The form “ἐσαεὶ” was preferred to render the meaning “forever”.
4. ἀναμιμνῄσκομεν: This form is in the active voice and means “remind someone of something”. It was replaced by the passive voice future tense verb “ἀναμνησόμεθα” which means “we will remember”.
5. σε: was replaced with the genitive “σου”, as the object of the verb “ἀναμνησόμεθα”, with parallel ascent of its accent on the last syllable of the verb.
6. ἐκείνοι ὅτι: were removed and replaced by “Ἡμεῖς, οἵτινες”.
7. Ἀλὶ: (<ἃλς=θάλαττα) it is a poetic form found in Homer, whereas the normal Attic word would be “θαλάττῃ”. It is up to you if you insist to retain the poetic form instead of the normal Attic one.
8. σᾶς διδασκαλίας: were removed and replaced by “τῇ σῇ διδασκαλίᾳ” in the dative case, as the object of the verb “ἀκολουθοῦμεν”.
So, a text as close as possible to the Attic dialect would be as follows:
“Ὦ φίλτατε Μάρκε, χαῖρε. Ἀναμνησόμεθά σου ἐσαεὶ ἡμεῖς, οἵτινες ἐν ἀργυρᾷ θαλάσσῃ (ἤ Ἀργυρᾷ Ἁλὶ) τῇ σῇ διδασκαλίᾳ ἀκολουθοῦμεν.” or
“Ὦ φίλτατε Μάρκε, χαῖρε. Ἡμεῖς, οἵτινες ἐν ἀργυρᾷ θαλάττῃ (ἤ Ἀργυρᾷ Ἁλὶ) τῇ σῇ διδασκαλίᾳ ἀκολουθοῦμεν, ἀναμνησόμεθά σου ἐσαεὶ.” translated in English as
“Oh, dearest friend Marcos, be happy. We, who in the middle of a silver sea are following your teachings, shall always remember you.”