You're doing great!
Your sentence with Ni was correct. Ni describes where something is, but De describes where an action takes place, or how you're going to do it. I guess it's a "verb qualifier". Such as "Toshokan de benkyoushimasu" (I'll study at the library), or "Jitensha de iku" (I'll go by bike)
He can be like "towards" so "Mura he michi" (the path towards the village), but don't quote me on that one. I hear it pretty rarely.
Wa is used to introduce a topic and so forth, and Ga is used when the topic has already been mentioned. There's subtle differences between "Ramen wa, suki desu" (literally means 'as for ramen, I like it') and "Ramen ga suki", but Ga is very flexible and you'll pick it up over time.
Like you said, wo can introduce a verb, such as "Sakana wo tabetai", but in informal conversation wo is often dropped.
I noticed you didn't ask about No or Mo, so here's a crash course. Since you like grammar terms, No is a possessive. "Boku no hon" = My book. "Takeshi no inu" = Takeshi's dog. You can read it backwards, dog OF (no) Takeshi, or think of it as an apostrophe+s.
Watashi
wa, terebi
wo suki = I like TV
If you want to say "I also like TV", where would you put the Mo? Would you replace the Wa, or the Wo? You'll be graded on your answer
My advice to you is to listen and speak the language, don't analyze it with that subject/direct object crap. It was enough of a pain in high school English :P