Is it possible to have the main page *not* be the blog, but rather a Page of my choice? And have the blog be one of the page-tabs?

Thanks!

See Site Admin -> Settings -> Reading -> Front page displays

Thanks! That worked great. But... how can I get the blog to appear as one of the tabs?

There are 2 options under that setting

Front page displays
Front page:
Posts page:

Posts page = Blog page

Yes, that's what I thought--I tried that, but the blog page did not appear under the "Posts Page"--only the pages I had created were given as options.

You'll basically "assign" an existing "Page" page the role of being the homepage for posts. Create a blank page and choose that at

Front page displays
Front page:
Posts page: