1) are there any of you singer/songwriter types who have written some original music and then "published" your BIAB recordings through a commercial medium (like iTunes, CDBaby etc).

= Yes, and backing tracks for live performances too.

2) do you think it is possible to use BIAB recordings (rather than studio productions) to publish songs through iTunes or CDBaby as "demos" for the purpose of teaching songs for congregational singing to musicians leading music in churches (assuming the chord chart, tabs, etc will also be provided via on a web site).
= Yes.

Are BIAB recordings "good enough" to sell commercially as downloads, in general, and more specifically, for the application that I have described. (All of this assumes quality songwriting and skillfully created rendition of the song in BIAB).

= Yes

BIAB will not be the weakest link in any of these endeavors. The live instruments and vocals as well as post production will be.

BIAB will not make a poorly live instrument or weak vocal good. Spend the studio time money you save by using BIAB and creating tracks at home on hiring professionals for the things you do not do well. If you record quality, clean tracks and then have them professionally mixed and mastered by a 'real' professional, it will not matter whether the track is created 'live' or with a Biab real track or realistic midi instrument.

It would likely startle you to learn how many 'home studio' tracks are on mainstream album releases.

BIAB Ultra Pak+ 2024:RB 2024, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.