You're welcome. And no problem; I've been taking care of my own bearded dragon for almost two years now, and from the very start, I did a lot of research here at this site. So if anything, it's the people on this site who taught me everything. Great resource here if you ever have questions or concerns.
And yes, glad I could help with the pictures. He
is very cute. I got mine when he was just a month old; he was a little bigger than my index finger then. They're really cute when they're little, but they're just as cute (in a different way, maybe) when they're bigger. :]
And that's good to hear that he's back to his old self again. And yes, it's pretty expensive getting everything together when you first start out; but once you have everything, it's just a matter of a couple of bulbs here and there every six months or so. Oh, and food. Which gets to be pretty expensive, but things work out in the end hopefully.
As for the scratching at the walls, that's pretty common with energetic bearded dragons. Most of the time, it's because they can see their reflections in the glass or something interesting through the glass. It sounds like the rock wall has been a good solution, but if you're looking for something that doesn't take up too much space, you can try using reptile habitat backgrounds/wallpapers instead. You can buy them in the store (or just make/print your own), but they're pretty tacky sometimes. The rock wall looks really nice, and as long as you get a larger terrarium at one point, he should probably be fine.
Ah, that's a common predicament; the problem of having to purchase larger and larger sized terrariums over time, that is. It's true that it is not a good idea for a baby to be chasing around crickets in a large terrarium; makes catching them more difficult, and you lose track of the crickets. What you could do is feed him in a separate, smaller container/terrarium like you noted. But another problem some people have, outside of feeding, is that the space of a larger terrarium can (but not always) be intimidating for a small bearded dragon.
Fortunately, there
is a solution! If you would like to simply purchase a terrarium that you could use for when he would be of max size, that would be just fine. You would simply have to invest in a terrarium divider (or I'm sure you could find something that could act similarly around the house, as long as you make sure it can't be knocked over), so that you could section off parts of the tank until he grows bigger and bigger. Here's an example of a terrarium divider: (
http://www.herpsupplies.com/images///APPTDSU/TDTankDividerIllus.jpg)
Another issue you may come across if you should decide to use a larger terrarium is that generally it takes more heat (and a longer
UVB bulb) to fill the terrarium. You may have to invest in some new lighting fixtures and/or bulbs, and will definitely have to spend some time trying out different bulbs and testing temperatures. Even if you use a terrarium divider, you may still need to take this into account.
The minimum-sized terrarium for an adult bearded dragon is a 40 gallon terrarium (breeder), which is 36" x 18" x 16". The recommended size is a 40 gallon (long) or a 55 gallon terrarium, which are 48" x 12" x 16" and 48" x 13" x 21", respectively (the significant difference between the breeder and these two latter terrariums is the length; between the two latter terrariums, it's really just an inch of width and a few inches of height, which isn't too much of a difference--what's important is the length). So a 42 inch terrarium seems to be right between the 40 gallon (breeder) and the long/55 gallon terrarium, which is fine. 40 gallon (long) and 55 gallon terrariums may seem difficult to find in corporate pet stores (at least around my area), so you may have to look online or at smaller, local businesses.
As for when he's ready for a bigger size, it's really kind of just knowing when. I've heard some bearded dragons are intimidated by large terrariums, while some get along just fine in them. I guess it depends on the bearded dragon. He should have enough room in his terrarium to turn around without trouble and to move around. I would think you would want a length of a terrarium to be around at least twice the bearded dragon's length (from head to tail).
And no worries, I don't mind answering questions or making suggestions. If it helps. :]