Haibun in English generally have a ‘title’. That said if you don’t use them, don’t worry, it won’t cost you a thing.
The ‘prose’ portion is best when it is a ‘prose poem’. The prose portion needs to sing to the reader. That said, do whatever you wish. One open warning I do NOT correct grammar in haibun, and frankly, don’t require it. Do any spellcheck and grammar check before submitting. The prose, much like the poem(s) within it, has to be yours and yours alone. Style points will never be given. The style needs to be yours. Stylebooks, and I have them all, are not something I rely on for poetry or prose.
The haiku/senryu in your haibun IS the focus. Just plain obvious but without the poem what you write is not a haibun, no matter how wonderful the prose reads or the story it tells. Be aware that I will read the poem first every single time, and you should too prior to submitting. That said, the prose may alter the meaning or meanings of the poem for the reader. That would be a kool thing, but not mandatory.
IF I offer any suggestions you don’t have to take them. In fact, I only offer suggestions ‘after’ I have decided to select your work. In my own experience, I take a lot of the suggestions I receive from editors, but I am clear to them that what I write is mine and has to reflect the experience I want to communicate. I will respect your wishes without fail because I did not have the experience you had. I just read about it and guessed from your prose and your poem the totality of the experience, I can’t ever know it the way you do. Writing to please me will only hurt your work, and I don’t even do it in my own haibun. If I don’t select your work for any reason it does not mean it is not good or worthy. It always boils down to one person’s opinion.
Layout and other issues that sometimes put other folks off don’t bother me at all. All poets are walking ‘experiments’ anyway, so don’t assume your attempt at haibun has to look like anyone else’s and don’t let any topic scare you off from submitting. Important to note that if formatting can’t be transported to the website for any reason then we will work with you. Your call if works or not.
I may write more about the form at some other time, but this is all anyone should need to get started.