You can get page counts from OpenLibrary and word counts from the linked editions on Internet Archive. Of course the latter is only going to be for public domain editions and if you are focused on review sentiment (as a proxy for purchase desirability?), you are probably more interested in modern non-public domain editions. The other drawback to IA word counts is that you'll need to download the full text to get them, but if you pull down a compressed text-only file, it shouldshouldn't be too bad.
Here's the chain of links you need to follow:
- OL work page https://openlibrary.org/works/OL3686173W/Lorna_Doone
- OL edition https://openlibrary.org/books/OL13522117M/Lorna_Doone
- OL API https://openlibrary.org/books/OL13522117M.json
- IA page https://archive.org/details/blaclornadooneromanc00rich
- IA files https://ia600308.us.archive.org/9/items/blaclornadooneromanc00rich/
- IA text file https://ia600308.us.archive.org/9/items/blaclornadooneromanc00rich/blaclornadooneromanc00rich_djvu.txt
Counting words is as simple as:
curl https://ia600308.us.archive.org/9/items/blaclornadooneromanc00rich/blaclornadooneromanc00rich_djvu.txt | wc
34410 280815 1488652
So this edition of Lorna Doone is 687 pages with (approximately) 280K words. The word count is done over OCR'd text, so it will not be 100% accurate, but it should be close enough for this type of project.