[maratd]

It depends on what area you want to target. Big data would be a niche field. You would need to know your market. Your market being any niche market where big data is relevant. You then target players who are small enough to need your services, but not large enough to need someone full-time doing what you do.

A lot of people see freelancing as some sort of gateway to doing what you enjoy on your terms. I suppose that's half true. The other half is marketing yourself and building a client base. Both halves are necessary.

If you're willing to take a major haircut off your rate (both in terms of what you bill and the service fees you'll pay), you can get low-end clients on the freelancing sites. That should really be seen as training wheels though and not a permanent solution. Low-end clients pay less, give you more grief, and the projects are less interesting.