This is kind of tough. I don't remember a time before Godzilla. I literally grew up watching the movies. According to my mother, I was a master of the TV remote by the age of two and was a pro channel surfer and the thing that I finally stopped on was a Godzilla movie. So I don't even remember what exactly the first movie I saw.
The same could kind of be said for First Owned as well, since I can't remember which one I got first. And there's also the fact that the first ones were probably recorded onto VHS from renting copies. But the oldest store bought Godzilla movie I had was King Kong vs Godzilla... I think.
Subtitled is a bit easier. At the first G-Con I picked up Godzilla vs MechaGodzilla '93 bootleg VHS. But if we're talking non-bootleg then it would be the DVDs back in the early 2000's brought out by Sony and Classic Media. Some quick searching on blu-ray.com it looks like Son of Godzilla was the first DVD with Japanese language track and English subtitles.
With theatrical, I'm assuming we are not going to count movies at conventions, so it would be Godzilla 1998.
First seen: ????
First owned: King Kong vs Godzilla ???
First subtitled: Godzilla vs MechaGodzilla '93/Son of Godzilla
First theatrical: Godzilla 1998