Hi,
hope all is well.
I have taken a look at the app you linked to.
I have been working on a similar app - the autoreply via notifications.
So, I totally understand what you need. As at now, I have an app prototype that replies automatically with the word 'hello' to anyone who messages the regular WhatsApp on phone it is installed on.
It doesn't reply to WhatsApp business at the moment, but I will add that functionality since you need it.
If interested, just start a chat with me and I will send you the app, so you see what I am talking about.
Once convinced, we can then discuss exactly the features you want,then I will finally build the app as per your specification.
Since I have this app installed on my phone, I can also just record it in action, and send you the video.
I also do web development, so I can assist with the creation or connection of the app to your web service.
as for your question, I have written some long text to it, and it seems to just read them fine. so in my opinion it will do just fine.
However, we can test the limits of how many characters it can read.
Since I have already figured out the tricky parts of the app, I can complete the app in less than 30 days as indicated, if your requirements are as simple as you have stated.
looking forward to working with you on this one.