Newbie: My first project. Is my workflow correct?

Question

I'm a newbie, working with After Effects for only a few hours. I want to make sure I'm doing things properly. I started with baby steps with my first project as follows:
I created a 9 second composition and added a single photograph to it.
I see that AE comes with some cool animated backgrounds like "Apparition". I want that as my background. 
Now, I'm asking myself, "how do I add this background to my composition?". Well I double-clicked on it to see what would happen. It seems to have replaced my photo. Not what I wanted.  Oops! 
I had to wonder if there was some attribute within my photo layer that would allow me to add an animated background, but I could not find anything like this.
Then I wondered, "do I have to make the animated background it's own layer?". If so, how? 
The only way I could figure out how to do this was by adding a solid color layer below my photo, then double-clicking "Apparition". This created the background I wanted. But is this the correct way to do this?
OK, now I added a second photo and want it's background different, like the "Cinders" background. And I want this photo duration to be 6 seconds.
When I added my second photo (photo 2), I had the CTI at the start, so photo 2 starts at the same time as photo 1, not what I wanted. I also discover that my timeframe does not extend beyond 9 seconds. Now what do I do?
OK, I set the composition to 15 seconds via Composition Settings. Then I drag my photo 2 layer bar I guess you call it, to start at the end of photo 1. Now I position the CTI at the start of photo 2 and add a solid color layer below it.
To my surprise, the solid color layer starts at zero, not at the CTI!   So, now I have to drag it over to line up with photo 2. Isn't there a better way? Anyway, I add the "Cinders" background and now have what I want.
Now I start to figure that a $1,000 program should have all kinds of features to aid you in the creation of videos. I find the Keyframe Assistant! Wow, let me start playing with this! 
I delete photo 2 and its background, leaving just photo 1 and its background. I add photo 2 back again to the composition. Then I run the Keyframe Assistant with no overlap.
First I notice that my composition is not long enough to contain all of my layers, so I change the composition duration to 1 minute. OK, I see that the Keyframe Assistant shifted all the layers, each layer starting where the previous one ended. So I grab photo 1's background layer and drag it back to where it is supposed to be. The lesson to be learned here, I guess, is that you add your photos first, use the Keyframe Assistant, then add your backgrounds.
Then I notice something peculiar with photo 2's duration! It looks longer than photo 1's duration. Then I try, without avail, to quickly ascertain the duration of photo 2. I right-click on the bar hoping to see an option to view the layer duration.  Nope, not there!  The only way I know how to do this is by tediously looking at the start and end points of the bar in relation to the timeline. Isn't there an a easier way?
I find out that the duration of photo 2 is 15 seconds, the duration of the entire composition. So now I remember that when you add a photo, it's duration will match the composition settings duration that you set. So, for every layer that you create, do you have to go back to the Composition Settings and set the desired duration for that layer?
I'm learning a lot, but is my workflow correct, or are there much easier ways to accomplish the same thing?

Answer 1

I strongly recommend that you begin at the beginning and start here to learn After Effects.
Regarding some of your specific questions:
> Then I wondered, "do I have to make the animated background it's own layer?".
Yes.
The reason that the Apparition animation replaced the image in your layer was that you had the layer selected when you double-clicked the animation preset. This applied the animation preset to the layer. If you make sure that you don't have any layers selected when you double-click the animation preset, this will create a new layer and apply the animation preset to the new layer. Or you could create a new solid, as you did, and apply the animation preset to that layer.
Here's some basic information about animation presets.
> To my surprise, the solid color layer starts at zero, not at the CTI!
See the first note on this page, which describes the Create Layers At Composition Start Time preference.
> Then I notice something peculiar with photo 2's duration! It looks
longer than photo 1's duration. Then I try, without avail, to quickly
ascertain the duration of photo 2. I right-click on the bar hoping to
see an option to view the layer duration.  Nope, not there!  The only
way I know how to do this is by tediously looking at the start and end
points of the bar in relation to the timeline. Isn't there an a easier
way?
Select the layer and look in the Info panel. Duration is given there.
> So, for every layer that you create, do you have to go back to the
Composition Settings and set the desired duration for that layer?
No.
"The Still Footage preference setting (Preferences > Import) controls the default duration of layers that use still footage items as their sources. By default, when you create a layer with a still image as its source, the duration of the layer is the duration of the composition. You can change the duration of the layer after it’s created by trimming the layer. "
(from After Effects Help)
Again, I strongly urge you to begin at the beginning and start here to learn After Effects. Work your way through the basic materials first. It makes everything else so much easier.