Going from stereo to mono only doubles the recording time if you are using an uncompressed format. The WMA format uses the high correlation between the two channels to achieve some of its compression. Therefore you won't get as much of a gain by going for mono.

I'd like to record daily life for a few weeks, for fun and profit (no profit, actually), but these things seem to need their batteries changing after only a few hours. Are there similar devices whose charge will last days or weeks?

With its pretensions for quality, why on earth doesn't it have FLAC? Same as uncompressed .wav, but approx. three times the capacity!

The amount of CPU power required to do real-time FLAC processing would flatten the batteries unfeasibly quickly.

...is some bundled software that transcribes your dictation. Unless I'm missing something none of them do?

What - more processing required than encoding to MP3 or (especially) WMA?