If it is possible, I would like a 3rd download option of just the files (in their respective folders) that have been added or changed in the SDK since the previous release. This would make a much smaller download to get an updated SDK.

Hello!
This type of download can be performed via GitHub

Do you mean that the plane could be moved to each of the six corners of an invisible cube (in front of the camera)?

You can for example use set of viewport aligned empties and Move To to relocate your aircraft

Regarding my larger objectives with this, I want to accomplish a few different things in a flight simulator game:

1) Planes should fly (Sounds simple, but I think it will be quite tricky. Evgeny has offered me some advice, but I'm still too much of a newbie to implement it.)
2) The planes should be able to shoot missiles and fire machine guns. Experimenting with methods for doing this was the purpose of this thread.
3) Missiles and other weapons should cause damage. I haven't reached this point yet.

I have an advice for you!
You can start from simpler app that can be made using logic editor without going crazy. Runner arcade mechanics comes to my mind. You can for example divide screen in six areas and move your plane/spaceship between them, fire missiles by clicking viewport aligned buttons (see b4w 15.12 features). There is excellent example of similar mechanics in our new year contest entries:
https://www.blend4web.com/en/forums/topic/1275/?page=1#post-6423
You will be able to focus on things like missiles animation, their interaction with targets and overall game look. And the final app will be solid and attractive itself.

After that you can begin to add freedom to your game using already made templates. We can provide support in adding JavaScript coding. Our engine apps structure is rather straightforward and clear, so even people who not familiar with programming can learn it quickly, especially if you understand logic trees tricks. Of course if you are interested in it!

Again it is just my vision of convenient and enjoyable way of developing your idea

Hy i had a look at it this afternoon and i came to the conclusion that in world space you go somewhere in the world space. So unless you move again to another place going to the same space again won't involve any movement. But in local space the object is always a it's own origin so x=1 is always 1 unit further. So to move every time you shoud use the local space.

You are absolutely right!

Not sure about parent though i didn't look yet

In Parent Space parent's location, rotation, scale are set as origin.
So for example if parent is static the only difference between World Space and Parent Space is initial offset.

This is currently way beyond my level of ability, so I have been doing some experiments and trying to learn B4W one piece at a time.

I think it is a wonderful starter project idea. There is no serious flight simulators of any kind yet on b4w. So it will be really interesting for us to keep track of your app and help to solve problems which you will face

One effect I have been able to achieve is creating a self-propelled missile that chases an empty in front of it. Since the empty is parented to the missile it remains in front of it forever, and the missile continues to chase it forever.
To my surprise, key-framing the empty to gradually get closer to the missile did not cause the missile to slow down over time.

Sorry, can't find any key-frames in blender. If i understand everything right, you want to animate empty to get missile move slower and slower with time. So you need somehow start this animation (apply default or with logic node or some other way)

This is good news that I could help with discovering a bug! No need to apologize.

Oh… forget to thank you for the help, of course! I am just really frustrated to have bug in such an important node.

I don't know how "on target" my approach is though in terms of being usable in a game, because none of this takes physics into account.

Move To takes physics into account. Physics properties for each object are declared in specific panel, you can find info in docs:
https://www.blend4web.com/doc/en/physics.html

I was not able to get the variable to accept a non-integer value. I tried 0.5, 0.1, etc. but it did not work. What is the correct way to do this?

I got it!
It is a terrible bug
If you use non integer variables for Y or Z translation/rotation their decimal parts will be ignored.

So sorry for that!
We'll fix it in the nearest release

Hello!

I would like to control the speed so that it gradually accelerates and decelerates

You can for example use variable for duration parameter in your transform node and increase/decrease it in loop

I would also like to be able to steer it using input from the keyboard.

For now there is no way to use keyboard input directly from logic editor. It requires JavaScript coding.

do you think is possible prepare a "pre-loading" as in sketchfab? The textures are heavy and I fear that people get tired to wait until the end of the load in order to play with the pieces.

There is no such option without using of JavaScript code. We are not 100% sure that it is useful but if there is real interest we may add this feature as flag passed to the webplayer (see "No social" flag in our current release features)