I am not sure about the real internal limits. BUT
Practically you may not be able to hit the limit of text, you will be most of the time blocked by network limitations. 
like 
if you are using GET request , your text-input will build large URL, and that will get truncated or refused due to URL length limitation. 
while using GET method always remain with 512 character limit.

Similarly if you are using POST method, I hope its safe to limit your request within 1MB,  mostly to make your app more responsive. 

The question about the punctuations is very interesting. With a little test i have (same text):

With punctuations: 62 entities Without punctuations: 65 entities