The tendency in many business is as you have described. It only pays if you reach a very large critical mass and you still need to get growing because at any moment competition may ramp-up their investment and catch up with your clients. They key here is to make this viral in so much as possible, that is, to use your clients to get new people joining - that allows cheap exponential growth.
Advertising and marketing is a different domain while gambling and money dealing is a different thing.
Those who are in finance are well aware marketing is not their cup of tea. So better have a professional who can take care of it. Hiring a marketing manager and guiding them a bit would be a great help.
If he is going to promote it here in the forum I think it is just a waste of resources to hire a marketing manager where he can ask a reputable manager to handle the promotion he can do here in the forum or are you referring to the manager here are the marketing manager? If you are referring to the managers here I think that's a good idea since they are more expert and more experience in marketing here.