Hi Lauren,
There are no known issues I’m aware of.
It’s simply a very difficult question to answer with a ton of variables. How many visitors/sec will you have at peak time … what server resources are available and how is your server configured (what server is it? Apache, nginx?) … are visitors likely to carry out actions that might be more resource intensive than normal … will query caching (and other caching layers) be implemented … we just can’t give an answer, I’m afraid.
I totally appreciate you want to go into this with your eyes open, but all I can suggest is either giving it a go (and having a strategy in place to scale out) or setting up a duplicate site and subjecting it to a battery of tests to see how it performs.
I know that isn’t a direct answer to your question but it’s the best I can do I’m afraid š