I definitely think it's worth having a website early on. A friend pointed out to me that it takes time for Google to 'find' (can't remember proper digital term) your website, so the earlier you start the more chance readers have of finding it when the time comes. At the start it probably only needs to be simple. I also think it helps to do it when you're not knee-deep in actual self-publishing tasks. Much easier to update a website you already have than to start from scratch when you're working on book edits and cover designs.