Ive nodeBB forum on ec2 t2.micro, nodebb and mongo are on the same machine,
do you know how much load / users it can handle ? ( plus minus aprox )
Probably not... but a good (if inaccurate) test would be to run ab against it from a different machine.
e.g. ab -c 100 -n1000
ab -c 100 -n1000