No. I can only imagine creating the text in Photoshop, rotating the document, and inserting this as a 'Photo'. (Book Spines are a problem only answered by finding fonts that are rotated )
2. to export as pdf in only 1 file (not separated cover file) ?
No. But there are programs (out there) that can join/merge PDF files. (or design pages 1&2 to look like a cover)
3. to have another book printing service than Blurb ?
Not through Lightroom-Classic. You can only Export the photos from a Collection and design elsewhere, or export the 'Blurb' book from the Book module as a PDF and send the PDF to other printing services.