Writing a book - best way to produce initial content?

[cartart]

Not sure where to start really?

I have a need to record (but not yet publish) the results of many years of important finds made whilst metal detecting an Iron Age site on a farm.

I need to use text, plotted maps, pictures of the coins/artefacts and diagrams.

Is there some online software or app that anyone has used to good effect? It would be put together and added to over the next 5 years at least.

When ready I would probably use one of those order and print on demand type companies?

If you can advise or help - thanks in advance

[cartart]

Thank you