Is basic functionality really free?

Good morning,
I find the functionality Snatchbot offers very promising, but I have a question regarding the pricing.

You say that for free plan, bot's users are unlimited and basic functions are included.

How many users can a Facebook Messenger chatbot have per month? Is there a limit of their messages? Is there a limit on number of free bots with such functionality per account?

Will upgrading for example one bot to Pro plan affect other bots created on the same account?

I am waiting for your reply,
Thank you