One page. Two pages. Eight pages. There is no right or wrong length for direct mail fundraising letters. Don’t believe what anyone tells you about this. Those are personal biases and likely not relevant to anything.
Take as many pages as you need in order to say what needs to be said. As long as your content is interesting, compelling and relevant, it can be as short or as long as you need.
I do agree with this “As long as your content is interesting, compelling and relevant, it can be as short or as long as you need”. Write what you wanna say and write it with sense.