I illustrated and co-published a picture book with an author friend of mine. We published through both KDP and IngramSpark (both print-on-demand) to get the best revenue, but the vast majority of our sales have come from in-person sales since it's easier outreach and we get to keep more of the profit from the author copies we sell. Because of the nature of the illustrations, we opted not to do an ebook and just stick with hardcover and paperback. So far the hardcovers have been the vastly more successful option.
As the illustrator, I illustrated the cover myself. We also didn't have any blurbs as we are debut self-published authors with no real connections yet. We did, however, offer a free virtual ARC to get reviews before our publication date, which served us well. (We had to publish early on KDP then list as "unavailable" to get Amazon reviews before pub day.) One of the reasons we self-published was because trad publishers don't typically accept author-illustrator duos, in favor of their own in-house illustrators, unless the author is also the illustrator, so trad publishing hasn't ever really been an option for us.
We've had decent success offering to do local school visits for free in exchange for sending home a flyer 2 weeks before the event with an order form on it. We collect order forms and money on the day, order the books, and deliver the signed copies about a month later. We have also been fortunate enough to get plugged in with some other local authors and get invited to join a local renaissance fair guild whose whole shtick is promoting books and literacy, so they've invited us to come sell our books at ren fairs with them and those have gone very well for us.
We have yet to break even on all of our costs (most books don't), but for a debut book, I'd say things have gone well in fostering an audience. We were a #1 bestseller on IngramSpark in our first week thanks to all the promo work we did leading up to release. We do plan to publish another book within the next few years. (I have a year left of grad school first which takes up most of my time.) We also have plans to self-record and publish an audiobook (looking at ACX and Findaway Voices). Our book also includes a song, so we're thinking of recording and releasing the song on Spotify, Youtube, etc. so folks who don't read music can hear how it goes.