Can I start by uploading a text-only version of an e-book (KDP, most likely) and later update the e-book to include the illustrations? This would let me get the story “out there” more quickly since the cover is almost done and I should only need one more revision pass on the text, but I wonder if that would be a strange thing to do.
Yes. One great thing about e-books is you can upload and publish new versions anytime. In your case, you might decide to make the two books distinct products, e.g. the regular version and the illustrated version. I caution you to make each version you publish a quality product, putting your best foot forward with what you’ve got to offer. If the book is really lacking without the illustrations, I would wait until you’re ready to include them. If not, then you might consider the “two editions” approach. One other consideration is that you want to avoid disappointing the buyers of the non-illustrated version, once the illustrated version comes out. You might want to offer the second version free or at a steep discount. It’s all about building and taking care with your brand.