Creating a new area after Kefka has been killed (FFVI Dragon's Den in FF3 US)

Boy, you sure are learning really fast...let's start step by step...

but I'm in that dangerous partially-educated stage where I regurgitate more than I understand.

I cannot stop laughing on this one

First, and please excuse me if my English fails to convey my intent, I wish to create a situation like the following:

1) Kefka is killed [bit xx is set, but Kefka remains a la Hidon for fighting whenever the fancy strikes you - this is just so the new area will become accessible]
2) New area becomes accessible by airship [display dialogue message $0B8D, wait for button press)
3) If ($Eventbit?($3-digit bit???)[$SpecificKefkaDead?, bit ?] is set, branch to $CA02D5 (pause for 120 units)
4) Choose 3 parties.
5) Load map $(I don't know how the maps are determined with the numbers, but I was going to use 0C7, 0DE, you know...)

My first problem is obvious: I don't really know what I'm doing, but that's why I'm asking. I'm going to mess up about 10.000 copies of FFVI before I get it right, and this is just the give me that first push.

The event in thamasa where the cave that leads to the esper mountain becomes accessible after strago talks to the party about the village of the mage warriors will be a great starting point for this part that you want to do. This event, after it has occurred, will enable the cave to the espers be open for you to enter it.

My guess is that, after you beat final kefka, you don't want to activate the event of the end of the game; instead, you'd like to warp the parties out of kefka's tower and give the player the message of availability of a new dungeon. This can be done, as you have guessed, by using event bits.

The game has bits that, depending on whether they are set or cleared, will let the "game" know when an event has occurred or not (at least I believe so...). These are used by if/else statements to activate events or stop the game from activating them. Which brings the topic of your next question...

Secondly, I've never seen a concise explanation of what something like this means:

CA/019B: C0 If ($1E80($127) [$1EA4, bit 7] is set), branch to $CA02D5

If you've seen if/else statements from any programming courses at college, this may make some sense. Depending on which events have taken place, the IF instruction asks the game: Has the event occurred? If it has, let's do the next instruction.

For that particular address, when [$1EA4, bit 7] is set, then the game executes the next instruction: "Load subroutine CA/02D5", or simply, "let's go to address CA/02D5, complete all actions, and return back to this point to continue executing other pieces of code.

Anyway, my question is essentially "How would I create an overworld airship event similar to entering the Phoenix Cave or Kefka's tower, but instead directing it to a map of my choosing, as well as ONLY having it be available AFTER Kefka has snuffed it?"

Good question, I actually don't know about this one. My guess is that you would need a bit to mark the first time someone enters the phoenix cave or kefka's tower. And, when it's the first time you enter one of these places, you'd like to load the map of the falcon with the party on top of it, and have a specific event unfold only once. That's where the IF comes in handy.