All beginning grammars start with the 2nd declension (the "o" dec. that you are referring to), then move on to the 1st dec. and finally bring in the 3rd. I'm using the "es" ending from the 3rd dec. as the most basic form. I will try to find some time to generate a video that works through the "o" declension specifically. The "oi" stem + ending is actually borrowed from the pronominal declension and thus even though it is the most common nom. pl. from it is exceptional.
Great question. I just added links to the app in the video description.
Yep, reading Campbell will confuse you, Jordan (but don't blame yourself). αὐτο βαλεῖ σε! Better read what Rugne's criticism of Porter before trying to understand Campbell who builds upon Porter. ἀλλὰ μῆπως δεῖ λέγειν πολλὴν Ἑλληνικήν. φιλῶ πολὺ οὗτος κινομάτος τοῦ Μάρκου καὶ Σέπ. οὺκ ἐθέλω ἁρπάζειν τοῦτον διαλόγον.
χαῖρε Μάρκος. φιλῶ κινηματογραφαί σου ἄει. οἱ λόγοι σου ἀληθεῖς. δεῖ με ποιεῖν κινηματογραφαί ἐν Ἑλληνικῇ πρὸς τὸν δήμιον. ἔχω ταῦτα τοῖς μαθηταῖς μου ἀλλὰ ὁ δήμιος οὐ δύνατι βλέπειν ταῦτα. ὅμως ποιήσω πολλοὺς ἐν Ἑλληνικῇ πρὸς τὸν δήμιον δι᾽ ὀλίγου.
You are right that I didn't mention words with accented long penults and how they will take acute or circumflex depending on the ultima. I will update that ASAP. (I do mention that in the first video, which I say a few times is prerequisite for this one.) I think that is the only issue that falls under "not everything said in this video is correct." If there is anything other than this one point that you find inconsistent or inaccurate please let me know. Thanks for the help.