As many as you need to tell the story and no more.
A short, punchy press release can sometimes cover all its news in 200-300 words, while a story needing more detail could run to 500 words or so.
What is important is that every word counts. If sentences ramble or contain incidental information that does not add much to the story, they could obscure the main message you want to get across.
Is there an absolute limit? No, although a longer press release must be enthralling or contain ground-breaking news to work. If it waffles or is stuffed with words and phrases that don’t move the story on, much is likely to be cut if a journalist has managed to read it all.
The test is to ask what every sentence or piece of information contributes. If it contributes nothing, cut it.