The problem with Publisher is that not everyone has it and so you make problems for people that would like to contribute. You can do most things with Word especially when you accept that it is just a drafting stage where you are getting all the ideas in the right order. So my suggestion is to concentrate on the content rather than the presentation at this stage.
I think it is a great idea to start with a guidebook. I suppose it can be a doc or a pdf. The important thing is that you can hone your ideas and get other people's input before going to the time and expense of coding it into an app. It will still be possible to make changes to the data of the app later but it is costly to change the structure of the app. Have you made a start with the guidebook that you could point me at. I don't find it easy to find stuff on this platform! Rod
Is Remind a text messaging service that is used in the United States? We also use text messaging in the UK. I agree with Melinda that it is a good idea to use an existing service. How would you like to see your idea turn into reality?