Interesting questions .....

As long as the pot your plant is in isn't sitting in water at the bottom of the cache pot, you're fine. If the pot fits the cache pot fairly tightly around the rim, I'm thinking that CO2 might build up in the cache pot, but methane & sulfurous gasses would diffuse because they're lighter than air (CO2 isn't). If the CO2 diffuses too, it's a nonissue.

I'm putting myself in your place and thinking about what I'd do, which is, let my plants tell me if they need some additional air circulation between the pots. Certainly, a little moisture in the pot is nothing to worry about, unless you know it to be wicking back up into the soil.

On a scale of 1-10 with 10 being most likely to be limiting, I'd put your concern about the residual moisture at a 1 and the potential for CO2 to be an issue at about a 3. Still, attention to details are what brings you closer to perfect plants. At any given time it's often the effects you aren't even considering that are most limiting, so it's always refreshing to see someone considering the details.

I like to point out that all our plants have the potential to be beautiful specimens, and the measure of how close they come is the measure of our ability to reduce or eliminate limiting factors to the greatest degree possible. IOW, how good we are at getting out of the plant's way! ;-)

Al

Thank you for the response!

The pots in most of the cache pots are raised by sitting on a piece of foam-stuff-I-had. This particular plant, being in a "bucket" is held up by the "handle" of the bucket that just slightly squeezes the rim of the plastic pot. You can see the gap here, and yes, it needs to be potted into new soil soon-ish:
{{gwi:41183}}

This is a very new plant, I just got it on Saturday. I took a picture of it so I can monitor its progress, so I will leave it as is for now and compare it to the starting condition to see if it seems to be doing well. It was a little bit pathetic looking when I bought it but I loved the color of the flowers and figured that (hopefully) it would only improve in appearance.

{{gwi:41184}}