Character Limit in iPhone Note

There are open source word document programs like Open Office and Libre Office that you can use. iCloud Drive is also available for you to use that is secure. Do you have a computer, or are you trying to do all of this on an iPhone? I would suggest using a computer and backing that information up to an external drive for archive. Office has a rather inexpensive subscription for minimal Office programs using the Home & Student version if you want to look into that.

I current use Office at my work and will be retiring within the next couple of years and have all of my work bits in my OneDrive. I will probably be getting a home subscription or will share one of the better subscriptions with members of my family and share the costs and then just transfer from the OneDrive of one to the other.

You mention saving the notes on your iPhone and backing up to iCloud. Why don't you just use iCloud Notes, since they are stored in iCloud then and available on however many devices you have logged into the same Apple ID. I would feel more secure that way. That is how I do it. I have access to my notes on my iPhone, iPad, and MacBook Air. Very easy to use that way.

I don't know that there is a limit, my guess it is based on available space on the iPhone. What exactly are you trying to save there that is not better served with a word processing document?