I tried nano tanks with bettas and it was sort of a pain to do water changes and all. A five or 10 gal is really better, and with a 10 gal you might even have a tankmate or two (not that bettas are easy to match to other species).
For just your one girl, I'd say a 5 gal is your best bet. They are small enough that a basic fluorescent strip is sufficient for most crypts, java ferms, mosses, marimo balls ... and bettas love plants so she'd be quite happy with her own little world.
I don't recommend dividing the riparium because a) it will never look right to you and b) dividers can easily fail when it comes to a determined betta trying to attack the one it sees on the other side. Males and females will absolutely savage each other, given the chance, and your girl may be interested in the male for very un-sexy reasons. Even with a succesful mating, bettas are typically only put together for a short period of time and then immediately separated after the event.
I can't really answer your other questions, but perhaps someone else will stop by who can.
For just your one girl, I'd say a 5 gal is your best bet. They are small enough that a basic fluorescent strip is sufficient for most crypts, java ferms, mosses, marimo balls ... and bettas love plants so she'd be quite happy with her own little world.
I don't recommend dividing the riparium because a) it will never look right to you and b) dividers can easily fail when it comes to a determined betta trying to attack the one it sees on the other side. Males and females will absolutely savage each other, given the chance, and your girl may be interested in the male for very un-sexy reasons. Even with a succesful mating, bettas are typically only put together for a short period of time and then immediately separated after the event.
I can't really answer your other questions, but perhaps someone else will stop by who can.