Yes, indeed, if you're looking to scale up to handle high concurrent user loads, scaling out horizontally is your best bet. We've got a client right now serving 700+ connections at the moment, and they're on four separate NodeBB instances. It's probably too much for what they need, but it's always nice to have more capacity than needed in case of spikes, etc.
What happened to the prettified numbers on your NodeBB?
I like full numbers, and here in the Netherlands we're not using 1k or 1m but full numbers. I made a topic and @frissdiegurke helped me with it to make it like this.