Novels start at 40,000 or 50,000 words. I go with 50,000, which would be a short YA novel. 80,000 is usually about the longest it will get, but there are exceptions. The chapter length is however long you want it to be. There aren't any rules.
And for writing descriptions - make sure they're as concise as possible, but still give important details. Mention anything unusual. Metaphors are great.