How long should the content of the page be?
How long is a piece of string? Honestly, there is no right answer to this question, but it is asked again and again. The content should be as long as it takes to cover the topic deep enough to rank.
But that's not too helpful, is it?
When creating content, you need to look at what is already ranked. Analyze at least the first 10 pages to understand the intent of the page and get an indication of how extensive your content should be.
But don't be obsessed with the length of the content! You should focus your efforts on creating content that responds to queries in the best possible way.