Are you knitting, as in using the knit button? If so, then you should switch to running blogdown::serve_site(), and be sure to delete whatever artifacts you're getting from knitting.
Re. configuration and TOML vs. YAML, see the blogdown book here (it links to the correct section, that just doesn't show up in the preview box):
I can't tell from the error, but is it possible you don't have the theme imported correctly?
Re. whether or not to troubleshoot, or re-build from RStudio with the recommended workflow, that's totally your call. You shouldn't have to, but sometimes it is easier to start from scratch. ¯\(°_o)/¯
I rounded up a bunch of blogdown posts I've found helpful here, if you're looking for more pointers (I don't actually offer any helpful advice, just links to people/posts that do!):